RADIO CONTROL OF MODEL AIRCRAFT

RADIO CONTROL OF MODEL AIRCRAFT

NEWNES

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It is an AppealIt is a genuine appeal to all men and women to do just that little bit extra; to make that extra

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By becoming efficient in your vocation you can give the best service to your country and toyourself. The more you increase your earning power the better it is for the country, and for yourself personally.

War or no war, earning power always brings its possessor to the front. It is no use waitingfor better times. The ideal opportunity never arrives. We have to make the best of existing conditionsTherefore, delay is useless; it is worse, it is harmful.

YOU CANNOT MAKE MONEY BY SAVING. If you save 10s. per week for 10 yearsyou have only £260, but it you spend 2s. 6d per week for 12 or 18 months on a correspondence course,you give your brains a chance to earn thousands of pounds, then there is no need to save. Savings are likelyto vanish, but earning capacity is a permanent investment.

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WAITING FOR1 list try t for yourselfTrace or draw the outlineand then put inthe features

There are nunareds of openings in connection withHumorous Papers, Advertisement DrawingPosters, Calendars, Catalogues Textile DesignsBook Illustrations, etc.60 per cent. of Commercial Art Work is done ti" Free Lance Artists " who do their work athome and sell it to the highest bidders. ManyCommercial Artists draw " retaining fees " fromvarious sources others prefer to work full-timeemployment or partnership arrangement. Weteach you not only how to draw what is wantedbut how to make buyers wan' what you draw.Many 01 our students who originally took upCommercial Art as a hobby have since turnedit Into a full-time paying profession with studioand stall of assistant artists; there is no limit tothe possibilities. Let its send full particulars for aFREE TRIAL and details of our course for yourInspection You wilt be uncle, no obligatiottwhatever

ejfe-4^1--t.4 c -e< ART DEPT. 76.

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DEPARTMEN r OF LITERATURE 16

Dept. 76, THE DEWITT COLLEGE, SHER laD

It you attend to this now, it may makea wonderful difference to vour future.

COUPON-CUT THIS OUT --...111111141k - - - -

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ti

November, 1939 NEWNES PRACTICAL MECHANICS 49

Deciding Factors...The DLP Vice -Screwing Machine should occupy acentral position in YOUR workshop.

Parallel Vice Pipe Vice Tube, Rod and Strip

Bender Cable, Rod and Pin

Cutter Screwing Machine Punching Machine Cable Stripper Flat and Conical AnvilsThe space required on yourbench is only 12' x 18".

The purchase price is but afraction of the cost of the

separate tools listed above.

AdaptabilityThe DLP Machinecombines the func-tions of all these tools,without loss of indi-vidual efficiency.

Compactness

Economy

Patent No.418,829

£5 . 17 6Illustrated

Folderon Application. '

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We keep in step with the times!SKYBIRDS new model is one of the latest FRENCH FIGHTERS-

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A "MILNES" LATHE is Essential

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ENGINEERINGWORKSHOP PRACTICE

This up-to-date book provides a complete practicalcourse of instruction in every important branch ofengineering workshop methods, materials and equip-ment. It deals with the underlying principles, crafts-manship, machines, tools, measuring processes andmachining methods of to -day, and it will prove indis-pensable to the engineer, draughtsman, mechanic,apprentice and engineering student. Its scope extendsfrom simple hand tools and machines to the latestelaborate machines and methods employed for mass -production purposes.

SOME OF THE SUBJECTSFiles, Chisels, Scrapers, Shears, Punches, Burnishers, Hand

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50 NEWNES PRACTICAL MECHANICS November, 1939

EPIGIATEERS!A 14 EQUIP YOURSELF FOR WORK OF

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Handbook contains, among otherintensely interesting matter. details ofB.Sc., A.M.I.C.E., A.M.I.Mech.E.,A.M.I.E.E., A.M.I.A.E., A.M.I.W.T.,A.M.I.R.E.,.Civil Service and otherimportant Engineering Examinations; out-lines courses in all branches of Civil,Mechanical, Electrical, Automobile,Radio, Television and AeronauticalEngineering, Building, GovernmentEmployment, etc., and explains theunique advantages of our EmploymentDepartment.

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THE first six weeks of war haveindicated the readiness and the

speed with which British people canchange from the comforts of peace tothe rigours of conflict. Motorists havebeen restricted as to the supply of petroland tens of thousands of them havereturned to the pedal bicycle. Enter-tainment has been restricted, and mostof us are now compelled to find ourevening entertainment at home. Weshall profit by it. A war throws intosharp relief the liberties we enjoy withpeace. Fortunately, most readers ofthis journal have practical hobbieswhich keep them keenly occupied intheir workshops and at home.

This is the time for home study. Aninspection of the list of reservedoccupations indicates the value whichthe State places upon those withpractical knowledge and training. Thiscan be rendered more valuable if youcan superimpose upon it a theoreticalknowledge. Such can be obtained in anumber of ways, and notwithstandingthe fact that many technical classes haveclosed down. Correspondence Coursesto day have reached a high standard ofexcellence. The moment is ripe to takeup a course in one or other of the manysubjects offered. It will bring a returnout of all proportion to the modest cost.

"More Miles Per Gallon"BEARING in mind that a large

number of motorists use their carsfor business and only to a minor degreefor pleasure, I have just written a specialbook entitled " More Miles Per Gallon."In it I deal with all methods of securingpetrol economy, including the factorsaffecting miles per gallon, engineefficiency, the use of Pool petrol, tuningthe carburetter, jet sizes and m.p.g.,fuel consumption and driving methods,decarbonising, adjustments, the effectof lubrication on petrol consumption,makers' economy recommendations,petrol dopes, running on paraffin,and the use of alternative fuels. This

PRACTICALMECHANICS

Editor: F. J. CAMM

VOL. VII. NOVEMBER, 1939. No. 74.

FAIR COMMENT96 -page book is fully illustrated, andcosts 1 s. or 1 s. 2d. by post from thePublishers, George Newnes, Ltd.," Tower House," Southampton Street,Strand, W.C.2.

The information does, of course,apply equally to motor cycles.

Practical Instructions

DURING the past month I have beenapproached by some hundreds of

readers and a considerable number ofmanufacturers to publish in this journala series of practical articles dealing withmethods of manufacture and workshopprocesses. Accordingly, I have arrangedfor the publication of a series of articlesdealing with the Lathe, the Planer, theShaper, the Milling Machine, Boring,Drilling, Screw -Thread Cutting, theDrawing Office, the Tool Room, Dyesand Press Tools, Gauges, Jigs andFixtures, Foundry Work, Pattern Mak-ing, etc., etc. It is pointed out to methat so many technical classes haveceased to function that I should makegood the omission. These articles willstart in the next issue in which I alsohope to be able to make an announce-ment of interest to all those engaged inthe engineering trades. These shouldnot overlook our two practicalvolumes, the " Practical MechanicsHandbook " 6s., by post 6s. 6d.; and" Workshop Calculations, Tables andFormulae " 3s. 6d., by post 3s. 10d.A catalogue of our technical books isavailable free of charge.

In this issue I commence publicationof a " Dictionary of Metals," which willbe of great value to engineers andstudents.

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The Wheels of ChanceG. WELLS' classic cycling

H . novel entitled " The Wheels ofChance," is appearing in serial form inour companion weekly THE CYCLIST.Charm is lent to this entertainingnovel by the fact that it deals with realroads and real inns. It deals with theadventures of Mr. Hoopdriver and theLady in Grey.

Now that so many readers are ridingbicycles, they will find this journal ofparticular interest. It contains the latestnews of the pastime, and a great amountof technical information on bicycles andaccessories. It is published everyWednesday at 2d.


RAD

Fig. 2. The portable field transmitter, controlbox, and the aerial tubes for 56 -Mc. operation

rOR many years the writer has hadmore or less of an ambition to operate byradio remote control some form of

movini, vehicle. But it has been only inrecent years that the ambition has beenrealised in the form of radio -controlledmodel aircraft.

Tice growing popularity of petrol -engine -d ri ven model aeroplanes influenced t liedecision to apply some form of control toreduce the hazards common to the usualpractice of allowing these models to takeoff, fly and land themselves. Many a proudowner has released his five- or six-foot wing -pan model, only to be forced to standhelplessly wringing his hands while itfinished its flight in a bunch of electricwires, or crashed in a mass of wreckage aftera long and losing argument with a carelesslyplaced pole or tree.

Powered with tiny two-cycle petrol enginesof from A to A. horse -power, according to thesize of the 'model, these 'planes are notcapable of carrying very much weight inaddition to that of the engine and ignitionaccessories. A number of radio -controlledmodels have been made, all over thecountry, but the usual practice has been tobuild a comparatively large 'plane of from

.8 ft. to 12 ft. wing -span, or even larger, toaccommodate the necessary apparatus forsteering and otherwise controlling it fromthe ground.

It occurred to the writer that the develop-ment, if possible, of equipment capable ofbeing carried in the more prevalent size ofmodel would be of more general interest andimportance. The aim, then, became to makepossible the ground control of model 'planeshaving a span of about 6 ft.

The " flying weight " complete of this sizemodel is usually around 3 lb. This loads thewing to about 10 oz. weight to the squarefoot of wing area. It was soon apparentthat models would fly very well with a-;neater wing loading than this. However,this is not generally done, since the common procedure is to limit the engine run bytimers which cut cif the ignition after10 to 30 seconds, after which the modelshould glide around for a considerablygreater length of time before landing.Loading them more heavily would result intheir gliding a somewhat shorter time afterthe engine was shut off.

It is during this gliding time that the

CO NT RO L FControlling a Model by Radio Reducesmon to the Usual Practice of Allowing a

Fly and Land by Itselfmodel is at the mercy of the breezes. Theymay cause it to drift into overhead wires,fences, or perhaps cause it to land in thewater. With control from the ground madepossible, the engine may be allowed to rununtil the fuel is exhausted-the averagetank carrying fuel enough to last from five toten minutes. Since the rudder may beoperated at will, the ship may be made tostay over the field.

Basis of the Contro.Motor torque effect, or the reaction Iron)

the turning of the prop., causes a tendencyfor models to lower the left wing and turnto the left more or less slightly, depending onthe model and the engine. All commonlyused engines are made to rotate in the

L,

3 TURN

CA

45 V.

vFig. I. The three -valve acorn receiver used in

the model plane

direction which causes a left turn. If thisturn is allowed to affect performance of themodel, it will climb. Opposite rudderingwill usually have the reverse effect. Theseeffects may be used to control the height ofthe model's flight, even though no control

r. c

TOSTEERING

MOTOR

I

NO cormccnoxr -- -1.s 955 CE, 1 F4 1,- 1

. I TO,,, HEATERS

Fig. 3.-Ground controlequipment

Oscillator UnitC1-35-mmfd. midget vari

ableC2-.003-mfd. midget micaR1-10,000 ohms, 2 wattsI.1-4 turns no. 14, d in. i.d.L2-1 turn no. 14, d in. i.d.L3-6 turns no. 14, 4 in. i.d.RFC 21.mh., 125.mA

chokeControl Box

R1-(Series resistor to in-terrupter) 30 -ohm rheo.stet

Si-Heater on -off switchS5-Dynamotor primary

switchI-Filament on -off indicator

.01119

TO DIPOLE ANTENNA

Lz RR 34

but the rudder is used. The first effort,then, was to develop a complete controlsystem simplified by being limited to thefunction of operating the rudder, so as tokeep the weight within reasonable limits.

The 'Plane ReceiversA type 30 valve seemed logical to start

with because it had a filament drain lowenough to allow operation from a very smallbattery. It was decided to operate on anultra -high frequency, so the transmitterradiating system mould be compact andeasily handled. For simplicity. the super -regenerative type of 'receiver seemed thelogical choice.

The signal response of such a detectorwould not ordinarily operate a relay fromthe plate current change available. . Theoutstanding characteristic of this detector,that of causing an audio hiss when idlingand losing this sound upon reception of a

C1-25-mmfd, air pad.der condenser

C2-.00025-mfd. micaC3-3-30-mmfd. mica

trimmerC4-.006-mfd. midget

micaC ,-.003-mfd. midget

MicaCa-.004-mfd. midget

micaR1-2 megohms;

wattR2 -200,000 -ohm

rheostat

R3-500,000 ohms, 4

wattR4-100,000 ohms.

wattR5-2 megohms,

wattR5 -6 -ohm midget

rheostatL1-13 turns no. 16,

in. i.d., tapped 3turns from plateend

RFC-21-mh.,125-MAchoke

Relay -8,000 ohms,s.p.d.t.

carrier, was used to change the bias on afollowing audio stage through a grid leakand condenser. This principle of operating arelay from the audio -stage plate -currentchange was borrowed from earlier experi-menters. The valve used for the amplifierstage is a high -mu type the American 11.4or its English equivalent works excellently-whose bias from the grid leak andcondenser combination limits its platecurrent to a very low value when no signalis being received. When a received carriersignal reaches the detector the hiss stops,the bias of the audio stage drops, and its

TO HEATER

SOCKET PLUG

OSC IL,LATOR UN IT

5,

- HUI.KEYRIGHT

RUDDER

CLOSED

'WitiTERRUPTER

CONTROL BQS,


MO E L

the Hazards Corn -Model to Take -off,

plate current rises to from three to fivetimes the no -signal value.

The writer's experience with the type 30valve on ultra -high frequencies has not beentoo good. The valves seem to reach acondition altogether too soon where theiremission is too low to super -regenerate athigh frequencies. This is particularly trueas the plate voltage used is limited to 45volts maximum to avoid having to carrytoo much weight in the form of high-tensionbatteries. The filament voltage has to beraised again and again, and the valve is soonuseless. For this reason the acorn type 955was next tried. The detector stage wascoupled to the audio with resistance insteadof transformed coupling to eliminate theweight of a transformer. The 955 super -regenerates easily at either 56 or 112 mc.through a 200,000 -ohm plate -couplingresistor which serves also as regenerationcontrol. It was found that varying the heatervoltage through a range of several voltsfrom normal had little effect on performance.

In the receiver used, shown in Fig. 1, a955 detector, followed by a 955 first audiostage fed a 1F4 second stage having asensitive relay in its plate circuit. Thepractice of earlier experimenters of adjustingthe detector for maximum hiss was followedat first with fair results. This is not the

By E. L. ROCKWOOD WEBB

most sensitive condition of the detector,however, so an experiment was made withthe detector just barely super -regenerating.In this case the last audio stage platecurrent was lowest instead of at a maximum.When a carrier was received, the currentwas decreased, instead of increased, causinga normally pulled -up relay to drop out to aback contact with signal.

With this arrangement the reception of asignal causes the plate current of the relaystage to change in a ratio of over 2i- to 1.The sensitivity is such that a 6L6 trans-mitter at a 33 -ft. distance, with no aerialon transmitter or receiver and only 42 voltsof plate on the transmitter, operates therelay stage through its full range of currentchange. Sensitivity seems to be at amaximum when the H.T. plus lead istapped down from the grid end of the coilabout three-quarters of its length, ratherthan having this lead connected directly tothe grid end, as is usually done with self -quenched detectors for 'phone reception.Fig. 4 shows a receiver of this type.

The primary object of the writer was tocontrol models of the size usually flown,rather than to build a special model to carrythe control. The usual petrol -engine -drivenmodel varies in size from those of 46 in. to48 -in. wing -span to the rather more un-usual sizes of 8 -ft. to 9 -ft. span. Thesmallest ones were impractical to carry acontrol, so it was decided to concentrate onthose of about 6 -ft. span. With the wingsremoved these may be carried fairly con-veniently in a car ; there are, of course,only certain places where it is practical to fly

LA N ES

Fig. 10.-The 5 -ft. biplane model which is equipped with radio control. The tuningmeter which is removed for flying can be just seen above the landing gear

them and they must be easy to transport.The receiver using the acorn valves, as

described above, was the fifth form of setwhich was constructed while efforts werebeing concentrated mainly on producing apractical, sensitive receiver. The drawbackto the set described was that the filamentrequirements were 6 volts for the 955's and2 volts for the 1F4. Total current require-ments for the acorn heaters and the 1F4are 360 mA. This drain necessitates the useof about eight penlite dashlight cells inseries parallel in order to get any satis-factory life out of the lir ater battery. Thisbank of penlite cells anu unts to a weight ofabout 4 oz.

The acorn receiving set weighed about7 oz., the relay 3 oz. more, and the H.T.battery from 9 to 10 oz., varying in indi-vidual batteries. If fresh when first pur-chased, the batteries will give better than100 hours' service life in these receivers.The first batteries purchased were dated ator before the date of purchase, so I didn't

Fig. 4.-Top view of the diminutive chassis ofthe throe -valve acorn receiver

get very good service from them. Theirshelf life is guaranteed at 6 months, butthere is so little demand for them that thedealer supplying them frequently hasthem in stock for some time before their sale.

The weight of the set may be decreasedby the use of the new acorn valves recentlybrought out, with a filament rating of 1.4volts at 50 mA. These were not availablewhen the above discussed set was beingworked out. This would reduce the filamentbattery weight requirements.Light H.T. Batteries

There are a number of light 45 -volt H.T.batteries available, but in the main theirshort life and the difficulty of obtainingthem makes their use impractical.

The line of Bantam valves produced bythe Hytron Laboratories might be used toadvantage. They are very small, and theirfilament drain is about 70 mA. at 1.4 volts.The line includes a detector triode, a high -gain pentode suitable to replace the 1F4,all designed to operate at 45 volts.

RelaysThere seems at present only one type

which is really practical for this use, theAmerican Sigma 2A or 3A. The onlydifference between them is that the 3Aoperates on 4 milliwatts power and the 2Acalls for 6 milliwatts. Either one has beenfound practical, as they both includedmeans of adjustment offering a response atquite a range of different current values.The 2A type was used by the writer, as thattype happened to be the most easily avail-able. It responds satisfactorily at as low acurrent as mA. The adjustments allowsettings which will cause the armature topull up and drop back with a current changeof as little as mA.

Control Transmitter DesignThe transmitter for field use offers quite

a bit of latitude for variation on the part ofthe constructor. Sixteen watts for outputseems a good value for reliable control, andthis may be obtained from an RK34operating at 300 volts. The power supplymay be obtained from either a vibrating

54 NliWNES PRACTICAL MECHANICS November, 1939

Fig. 5 (Above).-Top view of the steering controlshowing the double worm reduction. Fig. 6

(below).-Front view of the steering controlshowing the balsa -wood scotch yoke arrangement

reed rectifier or a 300 -volt motor generatoroperating, of course, from a 6 -volt storagebattery.

While a crystal -controlled transmittercould be used-perhaps with one section ofRK34 a 10 -meter crystal oscillator and theother half as doubler, followed by a finalamplifier-it will in general be found moresatisfactory to make final adjustments inthe field for resonance of the receiver withthe transmitter by tuning the transmitter tothe receiver rather than vice versa. So aself-excited oscillator transmitter has beenused for most satisfactory all-round results.The stability of a TNT circuit using theRK34 has been very good for this purposeas far as the writer has found. Any combi-nation of valve or valves delivering about16 watts to the aerial and operable from areasonably portable . power supply will befound satisfactory, provided that fairstability of frequency may be obtained. Nomodulation is necessary, hence the practic-ability of self-excited oscillators.

The Ground Control UnitAt first it was planned to build the

ground control equipment into a car as forportable mobile work. A slight practicalexperience in flying petrol models soonshowed this to be impractical in a goodmany cases due to the difficulty of drivingthe car close enough to the flying area of thefield, and to the fact that a car too closeto the models constitutes a flying hazard.Hence the portable battery:

Referring to Fig. 2, the case on the lefttopped by a carrying handle contains thebattery, an interrupter to be described, the300 -volt genemotor and a filter. The keyswitch at the left end of the top is thecontrol key which turned forward givesright rudder control, turned back gives leftrudder, and left in neutral causes the rudderto hold whatever position has been attained.This method allows the use of right or leftrudder to any amount desired, not in steps,and without a step. by -step selector systemwhich would necessitate putting the modelthrough successive unwanted positions toreach the one desired. Any position of thesteering mechanism may be reached fromany previous position-the rudder may he

reversed at will, no matter in what positionit -in Ay be.

The instrument on the left of the slopingpanel is an indicator showing when thefilament of the oscillator is on. Inthe centre is.. a millimeter in series withthe oscillator plate circuit. Above it is therheostat controlling the interrupter. Thecar dashboard ammeter to the right showsthe total battery drain. Above it is theknife switch controlling the 6 -volt inputto the high -voltage supply. On the rightend of the cabinet is a five -prong radiosocket into which plugs the rubber -coveredcord whose other end plugs into the oscil-lator case on the tripod. The aluminiumtubes shown standing against the case.plug into feed -through insulators on therear of the oscillator case. The case wasfitted with a nut underneath which fits thethreads of the standard camera tripod. Theaerial is a horizontal dipole inductivelycoupled to the oscillator tank, and is tunedby means of telescoping sections of theaerial.

The circuit of the ground equipment isshown in Fig. 3. As mentioned before, avibrating reed rectifier, or any source of300 volts D.C., may be used in place of thegenemotor. A method the writer has foundsatisfactory is to use two 200 -volt gene -motors with the high -voltage windings inseries and the 6 -volt connections in parallel,or even a smaller vibrating reed rectifier inseries with a 150 or 200 -volt genemotor. Inthis connection a word of caution-watchout for difficulties arising from the practiceof some .manufacturers of bringing thenegative high voltage and one side of the6 -volt lead to a common earth on the frame.The negative high voltage must not he

STMEMNGOTO.

WE *Ur)

Fig. 7.-RK62 receiver used in the model biplane

C1-25 'mmfd. air pad -der

C5-.00025-mfd. mid-get mica

C3-3-30.mmfd. micatrimmer

.05-infd., 400 -volt tubular

R1-4 megohms. Iwatt

R_ -15,000 -ohm mid-get rheostat

Li -10 turns no. 14,in. int. dia.

LRFC-Midget u.h.f.choke

Relay -8,000 -ohms.p.d.t.

131-Penlite cellB9-Midget 45 -volt

batteryB5, B4-2 penlite cells

in parallel

earthed, since it is to be connected to thepositive high -voltage lead of the other unitused in series with it. Using the RK34oscillator of Fig. 3, 80 mA. at 300 volts willbe required.

The Buzzer InterrupterThe interrupter shown in the cathode

circuit of the RK34 of Fig. 3 is made from amedium -size electric buzzer by soldering anextension about 4 in. long to the armature.A contact is placed at its extreme end tomeet another contact on a piece of lightshims brass. The shim is fastened parallel tothe armature extension and secured at theenf opposite to the contact so it will springslightly when contact is made. The buzzeris *rated from the 6 -volt battery and

controlled for most satisfactory operationby a series rheostat. The armature exten-sion is weighted at a point near the contactin a fashion similar to that employed on aVibroplex key. The weighting is done tocontrol the natural period of vibration ofthe assembly. A speed of contact as lowas two per second may be obtained. Thepurpose of this interrupter will be explainedlater.

The Steering MechanismOne of the surprising facts that become

evident to the builder of radio -controlledmodels is the fact that getting the actualreceiver working correctly in the 'plane isonly the beginning from the standpoint ofproblems involved. The attitude that it is allright to spend the time on the receiver andthen only work on the steering mechanismas a last-minute job must soon be correctedor there will be a batch of trouble in storefor the experimenter. The steering mecha-nism must be foolproof, absolutely reliable,unaffected by the vibration set up by thelittle one -cylinder petrol engines, and becapable of reasonably rapid response-notto mention one of the most importantconsiderations, that of lightness in weight.

The steering engine (top view, Fig. 5;front view, Fig. 6I is made up of a balsaframework upon which is mounted a Knappmodel railroad electric motor of the sizeknown as " HO " gauge. This drives aworm -and -pinion gear train with a ratio of500 to 1, ending up with a disc 1 in. indiameter on the second jack shaft. A pinnear the outer edge of the disc drives ascotch yoke. This converts the high speedof the little li-oz. motor into a compara-tively low horizontal to-and-fro motionwhich may be linked to the rudder througha length of stiff No. 16 piano wire. Themotor is reversible by changing the polarityof the armature current, the field being apermanent magnet.

Fig. 7 shows the diagram of the latereceiver using an RK62 thyratron detector.When a radio signal is received and therelay falls back, a contact is made by theSigma relay which sends, current throughthe steering motor in one direction, themotor increasing the rudder turn in a right-hand direction as long as the signal con-tinues. A release of the radio carrier allowsthe relay to pull up, reversing the currentthrough the motor by transferring toanother motor battery. The motor thenmoves the rudder to the left as long as thesignal is absent, until the limit is reached,when the frame of the scotch yoke opensswitch S, turning off the current and stop-ping the motor.

To stop the rudder at any desired pointalong its travel, it is only necessary to movethe key switch into neutral or centreposition. This position cuts in the inter-rupter incorporated in the transmitter unit,and the effect is to send out a pulsing signalwhich repeatedly reverses the steering motorat a speed such that rudder is preventedfrom moving in either direction. To getthis effect properly the interrupter isadjusted by the value of weight on thearmature extension until the pulsations ofsignal are just fast enough to keep thesteering motor from making any appreciableprogress in either direction, though it willrapidly move a slight amount first one wayand then the other. The rheostat in theinterrupter circuit is used to get thesmoothest action of the unit, but it has littleeffect on the actual speed of interruption,this being determined by the weighting ofthe vibrating arm.

(By Courtesy of "Radio")(To be continued)


How High Can W

A stratosphere 'plane whichhas reached a height of

nearly 50,000 feet

T0 the question, " What is the altitudelimit of human flight ? " the answeris that, in all probability, there is no

such limit, for if we had available a suitably -designed aerial -rocket capable of carryingpassengers, we could fly practically as highas we wished. As matters are, however, atthe present day the greatest possible heightto which it is possible to ascend by meansof a specially -designed balloon or aeroplaneis represented by the lower regions of thestratosphere.

The earth's atmosphere, as most aviationamateurs are aware, reaches upwards to aheight of nearly two hundred miles. Menof science nowadays divide the atmosphereinto four different regions : The Tropo-sphere, which is our " ordinary " atmos-phere consisting of the air we breathe, withits winds, clouds, mists and water vapour.Next comes the Tropopause, which is a sortof buffer layer, some two miles thick,between the troposphere and the Strato-sphere. The latter is the vast region of`ratified atmosphere consisting ye ncipallyof nitrogen, which extends upwards abovethe tropopause to a height of between fiftyand sixty miles above the earth's surface.Finally, comes the Upper Stratosphereextending above the stratosphere properand reaching to about two hundred milesabove the surface of our globe. The upperstratosphere is believed to consist mainlyof light gases such as hydrogen and helium,and its upper reaches constitute that ill-defined and still somewhat problematicalboundary between the earth's gaseousenvelope or atmosphere as a whole and thegasless, matterless void of outer space.The Upper Stratosphere

No human being has ever attempted tovoyage upwards into the upper strato-sphere, but many have been the endeavoursto sail into the stratosphere proper and toexplore its many perplexing and mysteriousconditions. With an ordinary aeroplane,no matter how well -powered and speedy itmay be, it is, of course, impossible to get upsubstantially into the stratosphere, sincenot only is that region of the atmosphere

devoid of sufficient oxygen to sustain humanlife, but it is, also, far too rarified to impartthe necessary amount of uplift to thenormally -designed aeroplane.

Indeed, an ordinary gas galloon has afar better chance of taking a man up intothe mid -stratosphere than any of the usualtypes of lower -level' aeroplanes, for, afterall, a balloon filled with hydrogen gas, thelightest of all material substances, willcontinue to rise to an enormous heightbefore eventually it bursts owing to theexpansion of the gas within its envelopeconsequent upon the increasingly reducedair -pressure without.

For many years previous to the inventionof the aeroplane, the exploration of highaltitudes by means of the balloon had pro -

Fly ?

tions he came to the conclusion that after acertain height has been reached (a height ofapproximately seven miles) the tempera-ture of the air no longer shows a steadydecrease with increase of height, but thatit remains practically constant at about50 degrees Centigrade below zero. It wasfrom these observations that Teisserencde Bort discovered that region of the upperair which we now term the stratosphere,the region which commences some tenmiles -above the earth's surface at theequator and about six and a half milesabove the earth at the poles.

Of very recent years, an enthusiasticgroup of Russian scientists have utilisedthe sounding balloon method of obtainingrecords of the earth's upper atmosphere.

THE PROBLEMS OF ULTRA -HIGHALTITUDE AVIATION OUTLINED

ceeded apace. Little scientific data, how-ever, had been accumulated, first of all onaccount of lack of sensitive recordinginstruments, and secondly in view of thefact that the early high altitude observersin mid-Victorian times found it impossibleto retain consciousness at altitudes muchabove five or six miles.

Scientists and meteorologists, therefore,evolved what is now known as the " sound-ing balloon," a balloon which is equippedwith various types of registering instru-ments and which is sent up into the higherregions of the atmosphere without anyhuman occupants whatever. When theballoon reaches a certain height, it bursts,whereupon a parachute automatically comesinto play and allows the instruments todescend to the ground unharmed.Sounding Balloons

The instrument -equipped sounding bal-loons were first used near Trappes, inFrance, in 1894, by an individualnamed Teisserenc de Bort. By analysingtwo or three hundred instrument registra-

They have even gone so far as to cause auto-matic radio transmitters to be taken up insounding balloons in an endeavour to obtainan accurate indication of the maximumaltitude reached by these balloons.Maximum Height Reached

Up to the present date, the maximumheight reached by any sounding balloonis twenty-three miles, that is to say wellinto the stratosphere proper. Temperaturerecords obtained with these balloons allbear out the fact that in the stratospherethe temperature is practically constant.Other records show, also, that in the strato-sphere there is no moisture, very littleoxygen and that the region is one of abound-ing ultra -violet light and cosmic rays.

Modern stratosphere exploration bymeans of lighter -than -air craft was estab-lished by the renowned Dr. Piccard andhis companion, Dr. M. Cosyns, who, onMay 27, 1931, ascended to a height ofabout nine and three-quarter miles. On asecond voyage (August 10, 1932) Piccardreached a height of ten and a half miles,


Stevens and Anderson in their stratosphereballoon in which they reached a height of

nearly 73,000 feet

whilst in the following year a Russianobserver, one M. F'rokofief, attained analtitude of practically twelve miles.

Air -Tight GondolaAll these ascents were made possible by

means of a very light, air -tight aluminumgondola of spherical shape which wasattached to the balloon, the observerstaking up their own oxygen with them andbringing back with them a considerablenumber of scientific records.

High as these altitude records were,however, they were greatly eclipsed onNovember 11, 1935, when Captain Stevensand Anderson; of the United States ArmyAir Colys, ascended in their stratosphereballoon, Explorer II. to a height of no lessthan 72,395 feet, or nearly 14 milesabove land level. This constitutes thehighest altitude to which human beingshave ever ascended, and although nodoubt this record will in its turn beexceeded, the feat of Stevens and Andersonin ascending without mishap to that un-precedented height is one which will notlightly be forgotten.

American BalloonExplorer II, the American stratosphere

balloon, had an envelope whose area wasno less than 2f acres, and when fullyinflated at the highest point of its ascentthe envelope was distended with 3,700,000cubic feet of helium gas, which gas, atground level, occupied a volume of 300,000cubic feet.

The ordinary aeroplane cannot, of course,hope to reach these colossal heights, for, inthe first place, the air at those altitudes is sorarified that it is unable to impart thenecessary degree of uplift and, again,because of the lack of oxygen at suchextreme heights.

The height record for an aeroplane isapproximately ten miles, a record which wasachieved by the Italian airman Mario Pezziin October, 1938. This height, of course, wasrendered possible by the employment of anengine super -charger and also oxygenapparatus for the pilot, for at that height

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24 STRATOSPHERE

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2/

20

/9

/8

17

16

/5

/4

/2

11

10

9

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43

2

HIGHEST SOUNDING -BALLOON ASCENT

neither man nor engine could breathewithout artificial aid.

Air SupplyThe problem of the air supply of an

engine at great heights has brought backonce again into the realm of aviation thesuggestion of the steam engine as a powerunit for high -flying 'planes. Despite thegreater weight of a steam power unitcompared with that of an internal-combus-tion engine of approximately ecu d horse-power, it is a simpler problem to supplyoxygen or air to a steam boiler at greatheights than it is to a petrol engine. Hence.when the nowadays projected " strato-planes " come into practical being, it is quitepossible that the engines of -some of themmay be steam -driven instead of petrol -propelled.

The firms of Farman in France andJunkers in Germany have, even at thepresent juncture, constructed experimentalaircraft for lower -stratosphere flight. Inboth instances sealed cabins have beenprovided in the 'planes for the pilot and hisobserver, whilst in the case of the Farman'plane an engine of some 400 h.p. was used,the carburetter taking air normally up toabout 13,000 feet. Above this leVel and up

-----

/4"aiagy ik ...I'

STRATOSPHERE''-OmILE.5__-

UPPER STRATO.),,200 MI LE5

HIGHEST POINT REACHED BY MAN(72,395Fr) STEVENS E. ANDERSON

NOVt. HT" /935

PROF: PICARD'SBALLOON

h1412/0 PEZZ1HIGHEST AEROPLANERECORD

LOWER LIMIT AT EARTHS

(Above) The four componentsof the earth's atmosphere. Thehighest altitude at presentreached by man or his instru-ments corresponds to the region

of the lower stratosphere

LOWER LIMITAT EQUATOR

MOUNT EVEREST(29./4/ FT

Illustration showing the comparative heights reached by different types of aircraft


to 25,000 feet a compresser was broughtinto action to feed air to the cylinders, asecond compresser functioning similarlybetween 25,000 and 60,000 feet, whilst athird compresser was arranged to operateat altitudes above 60,000 feet.

The design of the German Junkersmachine ran on similar lines, and by eitherof these planes it was intended that aminimum height of some 12 miles wouldreadily be attained and maintained.Variable Pitch Propellers

Such machines were designed withvariable -pitch propellers, the " cut " of thepropeller being made more acute as themachine ascended to stratosphere levels.Telescopic wings were also designed inorder to give the machines huge wing-spreads at high altitudes, these ultra -largewings being necessary in order to enablethe machine to ride on the intensely rarifiedair at heights of ten miles or more abovesea level.

Unfortunately for scientific research, warpreparations in several countries preventedthe making of sustained trials withspecially -designed machines of this type.Hence it would appear that all ultra -highflying and stratosphere research must neces-sarily be postponed until times of peaceagain return.

Although no ordinarily -designed planecan hope to attain the height of a strato-sphere balloon, it may, in the future, bepossible to design mechanically -propelledaircraft which will travel at enormousspeeds at heights well above the present-day limit for aeroplanes. After all, strato-sphere or lower -stratosphere travel, quiteapart from its enormous scientific interest,would, if made practicable, possess muchcommercial value. Owing to the rarity ofthe air at stratosphere levels, friction thereatis greatly diminished. Consequently aplane can be propelled at a far greaterspeed for the same effort than it can be atordinary air levels.

A stratosphererocket which wasdesigned to riseto an altitude ofmore than 300miles in less thanfive minutes

No Danger of IceAt the lower stratosphere levels, despite

the great cold prevailing, there will be nodanger of ice forming on the 'plane, sincethe air in those regions is perfectly dry. Atthese levels, also, the air is still and wind- -less, although, towards the upper limitsof the stratosphere it is now considered thatviolent storms rage and circulate. The lowerstratosphere is, of course, perfectly cloud-less and the sun is visible uninterruptedlyfrom its rise to its setting. Many of thebrighter stars are visible in the day -time,also. Hence, a commercial service of strato-planes operating, say, between England andAustralia or betwixt Europe and Americawould experience no navigation difficulties,for the only " blind flying " which suchpilots would be required to undertakebeing that involved in flying upwards ordownwards through dense cloud -belts whenascending into or descending from the lowerstratosphere.

The Upper EtratosphereTh, upper stratosphere, that entirely

unattained region of the earth's atmosphereexisting at a height of from approximatelyfifty to two hundred miles above sea level,will, perhaps, never be conquered bymethods of flight as we know them atpresent. No ordinary hydrogen or heliumballoon has ever reached the upper strato-sphere, so far as we are aware, and it is, ofcourse, impossible for any present-daypowered flying craft to attain that enormousheight.

It would seem, therefore, that if man isever to lift himself up to the level of theupper stratosphere he must await eitherthe coming of the rocket projectile or elsethe ultra -light plane which, propelled bythe as yet undiscovered atomic power, willbe capable of journeying upwards to theextreme boundary of the earth's atmosphereand of cruising thereat by means of energysupplies which are, at present, not merelyunknown, but also wholly undreamed of

An Engineering MiracleProducing Power from "Thin Air"

FOR startling effects of legerdemain,engineers of Ford Motor Companyand General Electric Company feel

that they have pretty well surpassed the-magician who produces a whole live rabbitfrom the apparently vacant atmospheresomewhere to the right of and above hisright ear. Instead of a mere rabbit theseengineers have produced some 2,500 to3,000 extra horsepower before the veryeyes of all present, and to make the analogycomplete they have produced these horsesfrom what may well be called " thinair."Trick of the Trade

Unlike the prestidigitators of old, theengineers are glad to explain the clevertrick of their trade which dispels themystery. It is the substitution of " thinair," or more properly, hydrogen, for airas a cooling medium for the armatures ofthe new 110,000 kilowatt turbo -generatorat the Ford Rouge Plant Powerhouse,Dearborn, Mich. Weighing only 1/14 asmuch as air, hydrogen offers far lessresistance. to the turning of the giantarmature, effecting a gain of 2i per cent.in power output at the 80,000 kilowattnormal " cruising speed " of the generator.That amounts to an output gain of from2,500 to 3,000 horse power per hour with-

out any increase of input energy. Althoughthe magician's rabbit may not legitimatelybe a creation of " something from nothing,"this feat of the engineering profession cer-tainly is.

The armature of the generator is enclosedin a sealed casing mounted on the armatureshaft through oil -sealed bearings. Thiscasing, or jacket, is provided with con-trolled valves at top and bottom. Thefirst step in filling the jacket with hydrogenis taken by opening both valves and pump-ing carbon -dioxide gas, which is heavierthan air, through the bottom valve untilall the air has been displaced. Both valveare then closed and the jacket is readyfor charging with hydrogen.Inlet and Outlet Valves

Hydrogen being lighter than air, theselection of inlet and outlet valves for thecharging is reversed. The top valve isopened and hydrogen is pumped in, carbondioxide being allowed to escape through thebottom valve until the concentration ofhydrogen in the jacket reaches 97 percent. Both valves are then closed. Stabilityof the hydrogen content of the jacket isensured by automatic gas analysing deviceswhich flash warning lights and audiblesignals in the event the concentration ofhydrogen falls below 90 per cent.

New GeneratorThe generator to which this Interesting

principle has been applied is the third110,000 kilowatt unit to be placed on theline of the world's largest industrial power-house at the Ford Rouge plant. Officialstarting of the new generator was accom-plished recently when William Clay Ford,grandson of Henry Ford, turned a Mer-cury 8 steering wheel to open the startingvalve. Companion unit to its two pre-decessors, installed in 1931 and 1936 res-pectively, the new generator embodiesengineering improvements which markedlyincrease its efficiency over the other units.With the new unit in service the capacityof the power house has been raised to462,000 horse -power.

Hydrogen CoolingEfficiency of the generator has been

increased by hydrogen cooling along prin-ciples almost identical with those under-lying the increase of automobile efficiencythrough streamline styling. In other words,both are problems in which the resistanceof a moving body to the medium throughwhich it passes must be reduced. In thecase of the automobile the solution hascome through careful wind -tunnel tests todetermine changes of external design whichwill allow it to move through the air witha minimum of wind resistance. A similarprocedure could not be followed in thecase of the generator, but an identicalresult was obtained by the substitution ofthe much thinner medium through whichthe armatures must move.


THE MONTH IN THE WORLD OF-

SCIENCE AND INVENTIONTelevision in War'Planes

ANEW YORK newspaper states thatItaly has now fitted a squadron of

war 'planes with television sets. Previousdifficulties due to the weight of the televisioninstallation and necessity for very stronglight have now been overcome.

They state that the installation has beenreduced to " flying " weight and that thetelevision set will now work in ordinarydaylight.

The first experiments carried out werelimited to the transmission of cloudformation pictures to a ground station, butit is now claimed that it is possible torecognise the make of a car travelling alongthe road from an aeroplane flying at aheight of 6,000 ft. It is possible to attaina television range of 100 miles. Experi-ments in this field of television have beenin progress in other countries for sometime.

England's Oldest WatchDURING the recent alterations to the

Cloister Garth of Canterbury Cathedral,a Saxon 10th century pocket sundial ofjewelled gold and silver was discovered.

the sun so that the shadow falls down itscolumn. The higher spot will be reachedby noon, and the lower at 9 a.m. and 3 p.m.

Hunting For Cosmic RaysDR. ROBERT A. MILLIGAN, of the

California Institute of Technology, hasrecently set out from Los Angeles on a cos-mic ray hunting tour of the Equator andadjacent countries. His equipment willinclude the world's smallest radio station,and 225 balloons. The balloons are capableof reaching a height of 20 miles and theywill be released in Australia, New Zealand,the East Indies, India and Egypt. Theballoons will carry delicate recordinginstruments up to altitudes which receive

FIRST DAY COVbiZ,

The first coal gas -driven car in England since the start of the second Great War

It is considered to be the oldest watch in the full force of the bombardment of thisthe English-speaking world. The workman- planet by the mysterious rays from outership is excellent and it consists of a silvertablet with a cap and chain of gold.

The gnomen, which consists of a goldpin, is surmounted by a delicately chasedanimal head with jewelled eyes. The headhas a ball in its mouth which when not inuse rests in a pocket at the lower end of thetablet. Abbreviated names of the monthsare inscribed in pairs on the faces and atthe top of each of the three columns is ahole for the pin when in use. Two spots aremarked below each hole.

To find out the time, the pin must beinserted in the hole appropriate to themonth, and the dial must hang free facing

space.

World's BroadcastingStations

T is estimated that there are aboutI36,000 broadcasting stations in the

whole world, of which about 8,000 are landstations, and the rest are mobile installa-tions in ships, etc. Of these 8,000 landstations, 1,800 are regularly used for enter-tainment, and the rest for communicationspurposes. Moreover, over two-thirds ofthese are American Stations.

Post Office Under theSea

SEATED in a globular, glass -walledchamber in the heart of a marine fairy-

land a small company of officials andprivileged guests recently witnessed anevent unparalleled in history-the openingof the Bahamas Sea Floor Post Office, theworld's first undersea postal depot. Theactual size of the post office is 6 ft. by 10 ft.,and it is a well yentilated chamber at thebottom of the sea.

Known as the Williamson Photosphere,it will also be used for broadcasting fromthe ocean floor, a powerful radio telephone

,Aft"4/111.---

F LO

3.0 103

A specimen postPl packet sent from the underseaPost Office, "Sea Floor, Bahamas"

making it possible to describe the wondersof the undersea as the sphere cruises throughcoral forests abounding in colourful sub-marine life. Mr. Ernest Williamson's sub-marine tube and Photosphere can thus betruly said to make the visions of JulesVerne come true. The mother ship forthe photosphere is the " Jules Verne III,"a strange craft from which is lowered theflexible tube and spherical chamber intothe sea.

A Gas -driven CarAN

illustration is shown on this page ofwhat is claimed to be the first coal

gas -driven car in England since the startof the second Great War. It has beenconverted for use with coal gas and LeedsCorporation have installed a special 4 in. gasmain at their depot in readiness for users.

The car can be used for either gas or petrol.A switch has been installed in the petrolcircuit and when gas is being used you justswitch off the petrol, or if you run out of gasyou just switch on the petrol. The owner ofthe car is having a crate made to fit on theroof so that the gas carrier will not swayabout too much.

Bags have to be used as the Governmentwill not pass the use of cylinders for a lifeof more than five years and the cost is toogreat as they are made of drawn manganesesteel. There is also the estimated outlay bythe gas companies of approximately £10,000to instal gas compressors and in presentconditions this is out of the question.


MASTERS OF MECHANICSInstead of journeys, people now

May go upon a Gurney,With steam to do the horses' work

By power of attorney.

Tho' with a load it may explodeAnd you may all be undone,

And find you're going up to HeavenInstead of up to London !

THUS Tom Hood, the comic poet ofa century ago, characteristicallyepitomised the credulous, suspicious

and half -humorous attitude which theLondon public adopted towards the pioneer-ing trials of Goldsworthy Gurney, theengineer and steam -coach inventor, to makepracticable a steam vehicle which would beof service for ordinary road use.

There were, of course, plenty of peoplewho were ready to say that a steam -propelled road -vehicle was impossible, thatsuch an invention, even if it did materialise,could be nothing other than a highlydangerous contraption, and that suchvehicles ought to be prohibited by Act ofParliament. But Goldsworthy Gurney andhis few contemporary inventors heededthem not. Instead, they concentrated uponthe problem of designing and constructing

Sir Goldsworthy Gurney, who invented a roadcarriage driven by steam

of metal tubes twisted roughly into theshape of a figure -eight. This boiler was onlypartially successful, but before long asecond boiler was forthcoming, the tubesof which were not welded but buttedtogether so that if any great internal steampressure arose, the tubes simple came apart,at their junctions. By means of such,tubular boilers, Gurney was able to get upwith safety steam -pressures of some 800 lbs.,despite the fact that the average steam -pressure in his later road locomotivesseldom exceed 120 lbs. sq. in.

In 1825, Gurney obtained his first patentfor a road locomotive propelled by steam.It was a somewhat curious contraption, for'its inventor endeavoured to work it withouta crank, utilising a pair of oppositely -placed"legs," which, in the words of the inventor,"are set in motion as the carriage ascendsa hill and move like the hind legs of ahorse, catching the ground and thusforcing the machine forward." Such asteam -coach seems actually to have beenrun on the public roads in 1827, but acouple of years later, Gurney completedanother steam carriage capable of accom-modating twenty-one passengers. It, also,had "legs," but it possessed pistons andcylinders, these driving the two rear wheels.

No. 5o. Sir Goldsworthy Gurney and theRoad Locomotives

a steam -driven road vehicle of such powerto enable it to ascend all ordinary roadgradients fully laden and without diffi-culty.

His Early CareerSir Goldsworthy Gurney-for he was

knighted by Queen Victoria later on in hiscareer-was a Cornishman, being born inthe Dutchy of Cornwall in 1793. Of hisearly education and training we know nextto nothing. He seems, however, like manyother Cornishmen of his generation, to havebeen attracted to engineering at a veryearly age, for in his youth he made mechani-cal models which really worked, models ofCornish beam engines and the like, whichpower units had at that time attained avery important status in the engineeringworld of the day.

Although Gurney, during his youngerdays, was not actually the first to hit uponthe now universal idea of the tubularboiler, he was one of the first to constructa light boiler made up entirely of tubes. Ina tubular boiler, of course, the water iscirculated through a series of heated tubes,an arrangement which permits of rapid andhigh-pressure steam -raising. Quite a num-ber of engineers of Gurney's day had beenagainst the principle of high-pressure steamwhen it was first introduced for locomotivepurposes by Richard Trevithick, anothercontemporary Cornish genius. James Watt,for instance, whose present measure of fameis, to say the least, out of all proportion tothe true facts concerning his career, wasstrongly opposed to all high-pressure steamsystems. So, too, was his unscrupulouspartner, Matthew Boulton. But Trevithick,Gurney and a handful of other locomotivepioneers and inventors persevered in the

face of all obstacles and eventually createdthe railway locomotive and the roadlocomotive.

Heating Coloured WaterGurney, at the outset, began by heating

coloured water in a circular -shaped glasstube provided with an outlet vent for thesteam. He showed that the convectioncurrents caused by the heated liquidenabled the latter to circulate, and, fromthis observation, he constructed his firsttubular boiler which consisted of a series

eginDlings of

A Successful CarriageThis latter road -carriage of Gurney's

was really successful. It made manyappearances in the environs of London, and,on one occasion, it actually made a journeyfrom London to Bath and back at an averagespeed of 15 m.p.h., a feat which, con-sidering the times in which it was made, istruly astonishing.

Just, however, as the pioneer railwayconstructors encountered severe oppositionto their labours, so, also, did -Goldsworthy'Gurney experience the same narrow par-'

Gurney's steom-propelled road coach built in 1839


tisanship which arose and threatened tomake an end of all his carriages. Indeed,on one occasion when Gurney was drivinghis steam carriage along a road near Bath,an attack was made upon the vehicle. Itsoccupants were actually stoned and Gurneyhimself was so badly manhandled that helost consciousness and had to be conveyedback to Bath for attention.

" Gurneys "Gradually, however, Gurney's activities

in the construction of road locomotivesprevailed. His vehicles-" Gurneys " theywere popularly called-came, for a time,into regular usage. For instance, in 1831,a regular toad service of " Gurneys "between Gloucester and Cheltenham cameinto operation four times per day. Theaverage speed of these journeys, stoppagesincluded, was approximately 10 miles perhour.

Other similar road -locomotives ran onregular services in London, and, for arelatively short time, Gurney appeared tobe heading rapidly for the utmost successin his pioneering activities.

Powerful interests, however, combinedtogether and eventually thrust the Gurneyroad -carriages and others from the roads.Such vested interests were by no meansonly those of the horse -owning and agri-cultural fraternities. Rather, the greateramount of opposition to Gurney's sch( mecame from the railways, who, having, a',that period, hardly established theirposition in the country, saw in the rise ofthe road -carriage a powerful competitorwhich would, if uncombated, defeat theirinterests and destroy,their coming monopoly.

Extortionate Road TollsAnd so it was that all these interests

combined together to pass through Parlia-ment certain Acts which, by way ofimposing extortionate and numerous roadtolls, made it quite impossible for the roadcarriages of Gurney or anyone else to carryon with any commercial measure of success.Steam carriages and, indeed, all forms ofmechanically -propelled vehicles were drivenoff the English roads until, towards the endof the century, the invention of the internal-combustion engine and its adaptation toa road -vehicle resulted in the rise of themodern motor car and the rapid removalof the various Parliamentary Acts whichfor more than sixty years had kept allpower -propelled vehicles off the highwaysof Britain.

Disappointed as Goldsworthy Gurneyundoubtedly was at the eventual lack ofcommercial success of his steam roadvehicles, their failure did not break him.He ceased to construct steam engines athis own expense in 1832, although forsome years afterwards he made efforts tofloat a public company for the constructionand operation of such vehicles. This projectfailed, however, as, also, did the effortswhich Gurney made to bring together a" ring " or association of contemporaryroad -vehicle inventors and steam -carriageproprietors, as, for example, the renownedWalter Hancock, who ran steam carriagesin London, Francis Maceroni, the Manches-ter -born Italian who operated mechanically -propelled vehicles in the East End ofLondon and many others. Gurney evenmade petitions to Parliament on behalf ofhis inventions, but the forces, opinions andinterests of his day were entirely againsthim, and, so far as his road -locomotiveactivities were concerned, little else thanunbelief and bitter opposition greeted hisefforts at every turn.

Other Branches of EngineeringAs, however, we have seen, Gurney

refused to remain dismayed. He turnedhis attention to other branches of engineer-ing, and, having more or less washed hishands of mechanical road vehicles andlocomotive construction, he took up otherlines of engineering interest, becomingeventually renowned as a consultingengineer of high repute, and ultimatelymeriting for himself the honour of knight-hood.

Gurney attained some measure of fameas a mining engineer and as an ingeniousinventor of a variety of mechanical devices.About the year 1854, for instance, a number

Gurney's experiment onthe heating of Water ina circular tube. Uponthese experiments Was

based Gurney's inven-tions of his tubular

boilers

of illicit distillers wereplying their unlawfulactivities in the neigh-bourhood of Stirling.They erected their plantin a lonely part of theestate of the SouthSauchie Colliery, nearStirling town. For a considerable periodthis " whisky gang " operated secretlyand successfully, but one day theirstill boiled over, the alcohol vapourscaught fire, and the burning liquor flowedin a stream down into the colliery workings.Here it met with fire damp. An explosionresulted, the illicit distillers flew from theplace. and the result was that the colliery

7 , z

h

STEAMVENT :!!'

workings became the scene of an under-ground conflagration which, for years,refused to become extinguished.

An Underground FireMuch damage was caused to underground

coal seams by this " burning waste ofClackmannan," as the area became known,until Goldsworthy Gurney, the engineer,was approached in the matter, he havingpreviously successfully extinguished anunderground fire at the Astley Collieries inYorkshire.

Gurney's plan was to use a high-pressure jet of steam and, by means ofthis, to force down into the mine workingsa large volume of " choke damp " ofsufficiently low temperature to cool downthe burning mass and at sufficient pressureto keep out the intlowing air.

To this end, a furnace was constructedabove ground and over it was erecteda high-pressure boiler. Flues and pipesconveyed the steam and gas to the under-ground workings. Carbonic gas, generatedby the furnace, was flooded into the mine-workings under steam pressure for severalhours every day, until, eventually, afterseveral weeks of these operations, it wasfound that the subterranean inferno hadbeen entirely cooled down and permanentlyextinguished.

As an engineer pure and simple, SirGoldsworthy Gurney has long been for-gotten. Indeed, it is only his pioneeringsteam -coach activities which has kept hismemory alive. In such respects, however,Gurney undoubtedly exhibited many of thetraits of genius. His tubular boilers, forinstance, contribute greatly not merely tothe making of road locomotives in generalbut also to rail locomotives. Stephenson,it is said, took several hints from Golds-worthy Gurney in respect of steam boilersfor high and maintained steam pressures,and, doubtless, many another inventorbecame similarly indebted to this nowadayslittle-known Cornish engineer.

Goldsworthy Gurney died in Cornwall,the land of his birth, in March, 1875, at theripe age of 82. He had lived a retired lifefor some time, but to the last day of hisexistence he evinced an amazingly keeninterest in all things mechanical.- What judgment posterity will accord tothe life and inventions of Sir GoldsworthyGurney is difficult to prophesy. The earlierportion of his career is, of course, the onewhich most entitles him to a niche in theFfall of Engineering Fame.

Another contemporary steam coach


SOFT SOLDERING HINTSTHIN STRIPSOF ZINCDROPPEDINTO ACID

HYDROCHLORICACID

Fig. 1 .-Chloride of zinc can be made by dissolvingstrips of zinc in hydrochloric acid. A porcelain

vessel should, for preference, be used

OLDERING is an easy process if one isskilled to the rules, but even so-calleddecent mechanics fail hopelessly on

many soldering jobs. Cleanliness is thegreat thing, but not more important than a

hot " iron and the right ' flux." It isnatural that the parts to be united shouldbe clean, and unreasonable to expect hotsolder and flux to remove refractorymaterial whose melting point is above thatof the iron or at once oxidises when heated.

Oxygen is the enemy of all forms ofuniting metals, as nearly all metals absorboxygen readily on the temperature beingraised, and it is to protect the metals frombeing oxidised that fluxes are used. Anexcellent flux for one metal is not so effectiveon another, or for some reason cannot beused owing to after effects which cannotbe eliminated. As an instance, acid fluxesmust not be used on electrical connections.The electrical flow sets up some form ofelectrolysis definitely aided by the minuteimprisoned particles of acid, which particlesare never entirely removed, however efficientthe washing of the part in question.The Main Fluxes

Chloride of zinc, resin, and Fluxite are themain fluxes used on repairs. The formeris a liquid and resin is used powdered.The easiest way to make up chloride of zincis to dissolve thin strips of zinc in commer-cial hydrochloric acid. Do this slowly in anopen porcelain basin until the acid will nolonger " act " on the zinc. When cool, thesolution is ready for use, and it should notbe adulterated with water. The action ofthis flux not only helps to clean the job, butthe moment the hot iron touches it, itentirely covers the spot without furthertrouble. When cold, it rests on the surfacein isolated globules, but the heating trans-forms it into a liquid coating, thus excludingoxygen from the air, that is unless the heatis too great and the flux is evaporated. Asan iron too cold will not run the solder, soan iron too hot will counter the effect ofthe flux. A small iron over -heated will not,and cannot, take the place of a larger ironwhich, if anything, is on the cold side.This flux is used on all tinned goods andarticles, such as petrol tanks, autovacs,

A Practical Article on the Elementary Principlesof Soldering

lamp bodies and petrol pipes, which are" tinned " before soldering.

Don't try to solder chromium plating, asit cannot be done. The chromium must be

PIPE

SOLDERFILLET -

SOLDERINGIRON

NIPPLE

WOODENBLOCK

Fig. 2.-The correct method of soldering a nippleto a pipe

removed before the solder will take, what-ever the flux. Aluminium is only success-fully soldered by the professional, and thenwith special solder and flux. It is not easy,and is often unsatisfactory. An excellentpreparation based on zinc chloride is agood soldering fluid. It is better and

POINTS TO REMEMBERMake sure that you are using the

right flux.

Chloride of zinc, resin, Fluxite andBaker's Fluid are the main fluxes.

Many failures are due to the ironcooling off before it can 4o any effectivework.

Always keep the iron well "tinned."

cleaner than the home-made product andequally as cheap in the long run.

Resin is a difficult flux at all times,therefore Fluxite (a paste) is far betterfor general use in every way, and is men-tioned because it is based on resin and isideal for all electrical joints.When the Iron Cools

Many failures are due to the iron coolingoff before it can do any effective work, the

Fig. 4.-When soldering two wires together, anefficient joint can be made by using sleeving

over the two ends as shown

job carrying off the heat when the iron isapplied. The larger the iron the better, asit must hold more heat, also repeatedapplication of a small iron means that theapplied heat is flowing away whilst thesecond heat is being added. Hold the ironstill when once applied and watch the effectof the molten solder around it. The soldercannot be rubbed in-it must flow of itsown accord. Solder has little strength as ametal, therefore always remember it as the" glue " that holds the work together only.Piling it on the job in the hope that it willovercome the difficulty or your poor work-manship is no use and only failure willresult.

Suppose a nipple is to be soldered on acopper pipe : first, the end of the pipe mustbe clean and really fit the nipple. The pipeshould just slide into the nipple with slightpressure. Dip the end of the pipe into theliquid flux and apply some solder with thehot iron. It will now be " tinned " and willhave cooled off somewhat. Again clip theend in the flux and tap on the nipple. This" tinned " end will act as a small iron andsave the trouble of having to " tin " thesmall interior of the nipple. Hold the pipevertically on a piece of wood with one handand apply the iron with the other hand.As the iron has again been charged withsolder, it flows from the iron on to the pipe,where it is already tinned, and so passesdown between the nipple and pipe.

A Bad JointShould the pipe have been a bad fit in the

nipple, the hot solder will not only havepenetrated between the pipe and nipple,but up the inside of the pipe also, not beingable to run out at the bottom on account ofthe wood acting as a washer. Should thishappen, the pipe must be drilled and theshavings from the drill blown out. If toomuch solder is applied, it is possible to wipeit off before cooling, but it leads to " blobs,"where they are not wanted, such as on thecone of the nipple, and perhaps a leakyunion. With practice, the right quantityof solder can be gauged, and if not enough,the iron can, in this instance, be appliedagain the second time, such process doublyassuring a tight soldered joint.

A patch on a tank is also an excellentexample of heat transmission by the solder-ing iron. As usuaL,clean the place on thetank thoroughly and " tin " the place to be

TANK UNDERREPAIR

------------

, - - -PATCH

Fig. 3.-When patching a tank make sure thatboth sides of the patch are "tinned," thus ensuring

an efficient job


operated upon about half an inch all roundthe patch to be applied. The patch shouldbe tinned both sides, as the hot solder onthe outside helps to convey the heat fromthe iron to the patch proper, and so to thesolder under the patch. The hot iron,supplied with solder, should be slowly andsystematically moved over the whole of thepatch so that it sticks to the tank at everypoint, and towards the end the iron isapplied to the edges, when, if there is stillany air under the patch, it will be seen tobubble out through the molten solder. Theiron should only be applied to the edgeslast of all, mainly to Make a neat job and toprove the exclusion of all air. Again, thelargest iron possible should be used,especially as it is not always possible to dothe job with one application.Electrical Repairs -

In dealing with all electrical repairs, it isagain pointed out that Fluxite or resin mustbe used and it is preferable to keep a specialiron for such repairs. An iron continuouslydipped in the liquid flux is bound to impartsome. of the acid to the electrical joint,eventually leading to trouble. Smear alittle Fluxite on the parts to be soldered, astoo much is not only a waste, but the surpluspaste has a tendency to mess up the nearbyinsulation. Cleanliness here is a definiteinjunction, as the Fluxite has no cleansingpowers like the fluid, and old wires thathave become blackened through burnedsolder must be cleaned with fine emerycloth until they are bright. Dipping thewires in nitric acid is fatal for the samereason mentioned with the liquid flux.

A spliced joint is out of the questionowing to the confines of the space allotted,also a sleeve -joint is far more efficient froman electrical point of view and occupies lessspace. Fig. 4 shows the sleeve, bored out sothat the prepared wires just slide into thehole. The ends of the wires will be seen atthe centre of the sleeve, where a slat hasbeen filed so that the hot solder can beapplied. Place a little Fluxite on the centreof the sleeve where the wires meet, andimmediately the hot iron and solder isintroduced, the Fluxite will run freely along

FLUXES FOR SOLDERING

Metals Fluxes Fluxes generally used

Iron Chloride of Zinc Chloride of zinc (killedSteel Sal -ammoniac spirit)Copper Chloride of zincBrass Resin

Sal -ammoniac ResinZinc (new)Zinc (old) Chloride of zinc

Lead (with fine solder) Hydrochloric acidLead (with coarse solder) Tallow and resinTin TallowPewter Resin and sweet oil

COMPOSITION OF SOFT SOLDERS

Solder Composition Melting point

Fine 1/ parts tin, 1 part lead 334°F.Tinman's 1 -part tin, 1 part lead ., 370°F.Plumber's

_

1 part tin, 2 parts lead 440°F.Pewterer's 1 part tin, 1 part lead, and 2 parts bismuth 203°F.

A mixture of 1 parts tin and 1 part lead fuses at a lower temperature than any othermixed proportion of these metals.

COMPOSITIONS OF HARD SOLDERS

Solder Composition

Hard brazingHard brazingSofter brazing"

3 parts copper, 1 part zinc1 part copper, 1 part zinc4 parts copper, 3 parts zinc, and 1 part tin

WOOD'S METALA special soft solder used for joining delicate pieces. It consists of 1 part tin, 4 parts

bismuth, 1 part cadmium, and 2 parts lead. It melts at about 60 degrees C.

the inside of the sleeve and between thestranded wires.

" Tinning " the IronTo " tin " an iron with either acid or

Fluxite, the bit should be cleaned up with afile until the copper is bright. Heat it onthe gas -ring until the copper is about tochange colour and rub with a stick of solderwhich 'has previously been dipped in theflux. Apply it quickly to all sides, after-wards wiping the solder over evenly with a

piece of rag. The iron is now " tinned "and ready for use, but there is anothermethod which is equally as good, and thatis to have a small piece of tinned steel onthe bench on which to rub the iron insteadof wiping it with the rag. Both methodsapply to both fluxes. When the iron is" tinned," it should still be carefully heated,as a " burned " iron ruins the tin on thesurface, turning it into a very brittle darkmass that will neither convey heat nor hbldthe solder.

Two Useful Soldering HintsA Workshop WrinkleIF when making a soldering joint, difficultyI is experienced in making the solder runinto the seam, the following tip may proveuseful. Clamp the bit in the vice, and drilla shallow 1 in. hole in the middle of theiron. Now, with a three -cornered file makea groove from the hole to the tip of the ironas shown.

When using the iron, place the stick of

A usefulsoldering

hint

solder into the bole, and it will be foundthat the solder will run down the grooveinto the hole.

A Soldering Blow -Pipe7 HE accompanying sketch shows aI soldering blow -pipe constructed from a

gas bracket. The nipple ends, on the gas andair tubes, were formed by hammering, thetubes being supported on a hollow blockduring the process. When sufficientlyreduced, the tube ends are reamered to size,the orifice of the gas -nipple being 18 in.diameter, and that of the air -nipple in.diameter. Flexible tubes connect the gas

WORKSHOP CALCULATIONSTABLES AND FORMULIE

by F. J. CAMMA handbook dealing with methods of calculation,solution to workshop problems, and the rules andformulw necessary in various workshop processes.It contains all the information a mechanic normally

requires

From all booksellers, 3;6 net,by post 3/9 from the publisher :

GEORGE NEWNES 'LTD. (Book Dept.),Tower House, Southampton St., London, W.C.2

Details of the blow -pipe

and air tubes to their respective sources ofsupply. While soft -soldering can beexecuted by blowing the flame with themouth, brazing requires the use of foot -bellows. When the air supply is derivedfrom bellows; a cock fitted to the air tubewill give better regulation of the flame.


A DICTIONARY OF

Metals and Their AlloysWhat this Dictionary Aims At

THE history of civilisation, and certainly that of industry,follows closely upon the history of metals and their alloys.Our modern age, both in peace and in wartime, is, without a

doubt, a metallurgical age, an era whose multifarious activitiesare based to a very large extent upon the production and usage ofvarious types and combinations of metals.

Yet, although metals have been known and used since historybegan to be recorded, it is a strange and significant fact that it isonly within the last fifty years or so that the science of metallurgyhas arisen. Formerly, the common metals were smelted fromtheir ores by rule of thumb methods which had been known forhundreds, and in some cases for thousands, of years, and the fewalloys which were of any practical import were, in like manner,produced by haphazard methods.

Necessity, however, is well known as the mother of indention,and it was virtually necessity coupled with the rise of appliedscience in the metal and engineering trades which was responsiblefor the enormous development in the science of metals and theiralloys which has taken place since even the commencement of thepresent century. ,

In spite of this advance, however, the science of metals and theiralloys is yet, in many respects, an infantile one. By no meanshave we penetrated anything like completely into the inner secretsof the metals. We do not kiaow exactly why the alloy produced bythe admixture of two or three simple metals may exhibit chdrac-teristics astonishingly different from any of the constituent metals.Neither do we know why a variation of as little as a tenth of oneper cent. in the composition of steel may create an amazing differ-ence in the characteristics and properties of the resulting metal.

Metals, in fact, are still, in many respects, a mystery to us, andmuch of the information which we have garnered about them isstill of the rule of thumb kind.

Nevertheless, slowly but surely the science of metallurgy iscreeping on, making new discoveries, nibbling away at the innermysteries of metals, so that, in the time to come, we may look for-ward to an age in which metals of strength and properties verydifferent from those of our present time are known and widelyused.

Abyssinian Gold. -See Talmi gold.Acid Bronze. -An acid -resisting alloy, some-

times used for mine pumps. Composition :Nickel, 1.50; lead, 17 ; copper, 73.5 ;tin, 8 per cent.

Actinium. -A radio -active metallic element.Chemical symbol, Ac ; At. No. 89 ; At. Wt.227 (7).. Discovered by Debierne in 1899in uranium residues. Little is knownabout it but it is apparently intermediatein properties between calcium and lan-thanum.

Admiralty Gunmetal. -A bronze having thecomposition : Copper, 88 ; tin, 10; zinc,2 per cent. Has a tensile strength of19 tons/sq. in.

Aeral.-An alwninium alloy of the com-position : Copper, 3.5 ; magnesium, 1.8 ;silicon, 0.6; cadmium, 2.25 per cent -remainder aluminium. Tensile strengthapproximately 30 tons/sq. in.

Aerolite.-A light aluminium alloy of com-plex proportions. Composition : Alumin-ium, 91.93; zinc, 0.12 ; silicon, 0.45;iron, 0.97 ; copper, 1.15 ; magnesium,0.38 per cent. Specific gravity, 2.74.

Aeron.-A modern aluminium alloy con-taining 4 per cent. of copper and 1 percent. of silicon. Is hard and strong.

. Can be heat -treated, in which state it willdevelop a tensile strength of 25 tons/sq. in.

Afinide.-French jewellery metal composedof nickel or German silver.

Age Hardening. -The property which cer-tain alloys possess of automaticallyhardening themselves when left for afew days at ordinary temperatures afterhaving been quelched in water. Changesin the grain structure of such alloysunderlie this phenomenon.

The reader who uses this present dictionary, however, can relyupon having at hand a mass of modern information on the subjectof metals and their alloys. Whilst the dictionary is no high-flowncompilation got together for the benefit of advanced students, theinformation which it contains will be found of use to even the work-ing scientist.

It is a remarkable fact that an alphabetical dictionary of metalsand alloys has never before been published in this present form.Many treatises and handbooks on descriptive metallurgy areavailable, but not one of them is arranged in such a manner as togive straightforward information with the least possible amountof trouble.

This dictionary, therefore, aims at meeting this need. Itsobject is to enable the busy and mechanically minded reader of" Practical Mechanics " to put his finger at once on the informationhe requires. Information which, for the purpose in view, is uselesshas been rigorously excluded from this dictionary in order to keepit within reasonable bounds. Yet every known metal is includedin the dictionary and almost every type of commercial metallicalloy.

Many very highly specialised alloys bear no specific name,these being simply represented by a series of code letters, as, forexample, ' P.66/7 alloy." Such alloys have been omitted fromthis present compilation, but in all cases the general type of alloyto which they belong has invariably been included. Thus, mentionis made of the famous " R.R." alloys, yet their various " Code -number " alloys have necessarily had to be excluded in view oftheir great numbers.

Sometimes, also, the reader may note that the percentages ofthe constituents of an alloy do not- add up to one hundred. Inall such cases, the difference must be ascribed to the presence ofimpurities which, usually accompany the alloying ingredients andwhich are not readily got rid of.

The dictionary is adequately cross-referenced. It is, in fact, ahandy and straightforward compilation of salient and useful factsregarding all the known metals and nearly all the known com-mercial alloys, and, as such it is presented to the reader in thehope that it will long remain a quick -reference compilation ofpractical use, instruction and interest.

LIST OF ABBREVIATIONSThe following abbreviations are used throffi.hont

this Dictionary :

At. No. ... Atomic NumberAt. Wt. ... Atcmic WeightM.P. ... Melting PointB.P. ... Boiling PointSp. 1;vay. ... Specific GravitySp. Ht. Specific HeatCoef. Ex p. ... Coefficient of ExpansionTherm. Coml. ... Thermal conductivityElec. Cond. ... ... Electrical conductivity

Aluminium -magnesium alloys andaluminium -copper -silicon alloys areparticularly susceptible to age hardening.

Ageing. -Metallurgical term referring to theimprovement in characteristics whichsome alloys undergo, particularly thoseof aluminium, after they have been keptfor some time. It is a process of metallicmaturing.

Aich's Metal. -Average composition : Cop-per, 60.66 ; zinc, 36.58 ; tin, 1.02 ; iron,1.74 per cent. It is hard and tough, and,being resistant to sea -water, has beenused as a sheathing metal for ship'sbottoms. It has a golden colour.

Air -hardened Steels. -These are alloy steelsin which a certain degree of hardness hasbeen induced merely by air-cooling undercontrolled conditions.

Ajax Metal. -An anti -friction bearing metal.Composition : Copper, 87.24 ; tin, 10.98 ;lead, 7.27 ; arsenic (or phosphorus),0.37 Parts. .1 The arsenic or phosphorusacts as a hardening agent.

Albata Metal. -Composition : Copper, 40;zinc, 32 ; nickel, 8 parts.

Alclad.-A metal consisting of duraluminwith a coat of pure aluminium rolled on.It has good corrosion resistance.

Aldal.-An aluminium alloy of the following

approximate composition: Copper, 4.0;magnesium, 0.5; manganese, 0.5; silicon,0.6 per cent -remainder aluminium. Ishard and possesses a tensile strength ofbetween 25 and 35 tons/sq. in.

Aldebaranium.-A name for Ytterbium,proposed by Auer von Welsbach in 1906.It is now obsolete.

Aldrey.-A modern aluminium -magnesium -silicon alloy. Composition : Magnesium,0.5; silicon, 0.6 per cent. -remainderaluminium. In this alloy, the magnesiumand silicon act as hardeners. The alloycan be heat -treated. Tensile strength,20-22 tons/sq. in.

Alfenide Metal. -Composition: Copper, 60;zinc, 30; nickel, 10 parts; plus traces ofiron. Similar to Albata metal. Isresistant to dilute acids.

Alferium.-A French aluminium alloy usedin aero construction. Composition :Copper, 2.5 ; magnesium, 0.6 ; manganese,0.5 ; silicon, 0.3 per cent. -remainderaluminium. Tensile strength about30 tons/sq. in.

Alger Metal., -A tin -antimony alloy. Com-position: Tin, 90; antimony, 10 per cent.

Algiers Metal. -A tin -antimony alloy, littleused nowadays. Composition: Tin, 90;antimony, 10 per cent. Sometimes con-tains copper, also. It is white and takes agood polish.

Alkali Metals. -This well-known family ofmetallic elements comprises the followingmembers : Lithium, sodium, potassium,rubidium, caesium. The name was sogiven on account of the strongly alkalinenature of the compounds (particularly thehydroxides) of these metals, as, forexample, caustic soda (sodium hydroxide).

Alkaline Earth Metals. -These are the


metals, calcium, strontium and barium-so-called because they are derived from" earths " (such as lime) which are alkalinein nature.

Allan's Metal.-A copper -lead alloy (or so-called " tin -free " bronze). Composition:

Copper, 55; lead, 45 per cent. Used forDiesel engine piston rings.

Allautal.-This consists of the aluminiumalloy, " Lautal," having a coat of purealuminium rolled on to it. It is corrosionresistant.

Alloy.-A mixture and/or combination oftwo or more metals forming an apparentlyhomogeneous mass. Alloys can be pro-duced by the simple admixture of themolten metals, by the smelting of mixedores, by electrolytic methods or by thecompression of mixed metallic powders.Alloys containing mercury are calledamalgams.

When metals are alloyed togetherthey (a) dissolve in each other in anyproportions but without actual chemicalcombination; or (b) chemically combinewith one another, such resulting com-pounds in some cases dissolving in theexcess of pure metal present; or (c)dissolve in one another to a limitedextent; or (d) remain undissolved in oneanother, in which latter case they willtend to separate out in layers when themetal cools.

The general effect 'of alloying metalstogether is to lower the melting point andconductivity, increase the hardnesa, andsometimes the strength of the metal.Colour changes often are brought aboutby alloying, and in many other ways, thepropertieff of the alloying metals are pro-foundly modified in the resultant alloys.

(The word " alloy " is considered to bederived from the Latin, alligo, to bindtogether.)

Alloy Steels.-These are, varieties of steelcontaining considerable percentages ofother metals, such as tungsten, chromium,nickel, manganese, etc., which have beenadded for the sake of increasing thehardness, strength or corrosion -resistanceof the metal, or for some other specialpurpose. Such steels are also known as

Special Steels." They are detailed undertheir individual names.

Alluvial Gold.-Gold obtained from sands,_ gravels and grits occurring on the beds

of ancient streams. The gold in suchlocalities usually takes the form of smallscales or rounded grains, and is knownto the miners as " gold dust."

Almag.-An aluminium alloy. Composi-tion : Copper, 2.5; magnesium. 0.7 ;silicon, 0.6 per cent., remainder alumi-nium. Tensile strength about 25 tonssq. in. Is very hard and enduring.

Almasilium.-A modern aluminium alloyof French origin. Contains i Magnesium,1.0; silicon, 2.0 per cent.-remainderaluminium. Can be heat -treated andhas considerable hardness. Tensilestrength about 22 tons/sq. in.

Almelec.-A recent aluminium alloy con-taining magnesium (0.7 per cent.) andsilicon (0.5 per cent.) as hardening agents.Tensile strength about 20 tons/sq. in.

Alnico.-An aluminium -nickel -cobalt steelused for making permanent magnetsand magnet cores. It offers a maximumamount of magnetic energy per unitmass of metal and, in this respect, con-stitutes a great advance on the oldmagnet steels. Composition : Steel. 604aluminium, l0; nickel, 20; cobalt, 10 percent.

Alpax.-An aluminium -silicon alloy, origi-nally invented by Aladar Pacz, afterwhom it is named. It contains 87 percent. of aluminium and 13 per cent. of

silicon. It is ductile and fine-grained, andhas a silvery -white colour.

Aludur.-A modern aluminium alloy con-taining 0.6 per cent. of magnesium and0.88 per cent. of silicon. It is heat -treatable and has a tensile strength of20 tons/sq. in.

Alumel.-A nickel alloy used in electricalthermometers and thermo-j unctions.Composition: Nickel, 94; aluminium, 2;silicon, 1; manganese, 2.5 per cent.

Aluminac-An alloy similar to Alpax,which see.

Aluminium. --Metallic element. Chemicalsymbol. Al; At. No. 13; At. Wt. 27;M.P. 657°C. ; B.P. 1,800`C. ; Sp. Gray.'2.58 ; Sp. Ht. .2253 ; Coef. Exp. .002313;Therm Cond. (Silver= 100) 31.33; Elec.Cond. at 0°C..(Mercury= 1) 20.97.

Chief ores : Bauxite, Cryolite and thevarious Felspars. Is a constituent of allclays. First isolated in 1828 by F.Wohler. Given its name by H. Davyfrom the Latin, alumen, alum, on accountof its presence in the various alums.Owing to difficulties in manufacture, themetal was not commercially marketeduntil about 1887.

Aluminium is a bluish -white metalcapable of taking a high polish. Exposedto air, it becomes covered with a finefilm of oxide. By suitable electro-chemical treatment it may be " anodised "or coated with an artificially-prOducedfilm of aluminium oxide, A1503, of greattenacity and fineness. This film may thenbe dyed, thus imparting a colouredsurface to the metal. Aluminium isfairly ductile And malleable, particularlyabove 100°C. At 530°C. the metalbecomes so brittle that it can be powdered.When ignited at high temperatures itburns brilliantly, an extremely hightemperature being attained. Upon thisfact is based the principle of " Thermite "welding. The metal is electrically posi-tive. It disolves in many acids and alsoin solutions of caustic soda and potash.Owing to its tendency to forth and retainan oxide coating, the metal is difficultto solder. Aluminium forms a largeseries of alloys with other metals, manyof which are nowadays of the greatestimportance. Cast aluminium has atensile strength of about 5 tons'sq. in ;when rolled. of about 12 tons/sq. in.

Aluminium Amalgam.-This is prepared byadding fine aluminium filing to a half percent. solution of mercuric chloride fortwo or three minutes, and afterwardswashing the product with alcohol orspirits. The resulting amalgam decom-ooscs water at ordinary temperatures.liberating a steady stream of hydrogen gas.

Aluminium Brass.-A variety of copper -aluminium alloys containing up to 5 percent. of aluminium. Uses similar tothose of aluminium bronze.

Aluminium Bronze.-A class of copper -aluminium alloys containing from 5 to11 per cent. of aluminium. They arechiefly of use in circumstances in whichit is necessary to increase the oxidationresistance of the metal. They have ten-sile strengths up to 38 tons,'sq. in.

Aluminium -Chromium Alloy.-Alloyedwith chromium. aluminium forms beauti-ful needle -like crystals. The alloy -isbrittle, however, and has no commercialapplications.

Aluminium Gold.-A peculiar alloy havingan intense ruby -red colour. Composition :Aluminium. 22; gold, 78 per cent. M.P.1,060°C.

Aluminium Steel.-Aluminium is not usu-ally alloyed with steel in order to form aspecial alloy, but in view of its deoxidisingpowers. Dissolved oxides in molten steel

tend to form blowholes. Aluminium.however, removes these oxides and socontributes to the homogen-ity and result-ing strength of the steel.

Aluminium steels were first investi-gated by Sir Robert Hadfield in 1890.With steel containing, say, 0.2 per cent.of carbon, aluminium may be added inamounts up to 5 per cent. withoutinfluencing the tensile strength. Thebrittleness of the steel, however, increaseswith more than 2 per cent. of alloyedaluminium.

There is a curious alloy formed withiron and about 17 per cent. of aluminium.This is non-magnetic and heat -resisting.

Aluminised Yellow Brass.-A variety ofbrass containing up to 1 per cent. ofaluminium. When aluminium is added insmall quantity to a brass, the zinc con-tent of the latter can be higher than whenthe aluminium is not added, thus makingfor a light-coloured brass. The followingis an aluminised yellow brass made forsaddlery and harness purposes : Copper,55.25; zinc, 41.25; lead, 3; aluminium.0.5 parts.

Aluminum.-The American rendering (pro-nounced " a-loo-mi-num ") of our word" aluminium." It is, perhaps, the morelogical word, since it more clearly indi-cates the fact that the metal is a con-stituent of alum.

Alumium.-An early name for aluminiumsuggested by Sir Humphry Davy in 1807.

Amalgam.-The name given to a solutionof a metal in mercury or to an alloy ofmercury with one or more metals. Mostmetals will form an amalgam with mer-cury, and often, as in the case of sodium -and potassium, the amalgamation isaccompanied by considerable rise of tem-perature. In other instances, as, forexample, in the preparation of tin amal-gam, there is an absorption of heatduring the process of amalgamation. -

Amalgams are much used in modernindustry and arts, as, for instance, in theextraction of gold and for the filling ofteeth.

American Gold.-American standard goldas used for 'coinage purposes contained90 per cent. of gold and 10 per cent. ofcopper, thus being slightly harder thanthe English standard gold on account ofits increased copper content.

American Nickel-Silver.-An old alloy. Itcontained : Iron, 1 ; cobalt, 1; silver, 2;tin, 2; manganese, 4; nickel, 24; zinc, 36;copper, 96 parts.

Ammonium Amalgam.-When a quantityof sodium amalgam is thrown into a dishcontaining a fairly strong solution ofammonium chloride_ (sal ammoniac), themercury swells up enormously into ametallic -looking, soft, sponge -like mass.This is often called " ammonium amal-gam," and it has been thought to consistof a true amalgam of mercury with the" ammonium " group or radical NH.).It is now believed to comprise ',relymercury, which is inflated by hydrogengas, for, after a few minutes, the masssinks down again, leaving metallicmercury at the bottom of the dish.

Amorphous Antimony.-A black powderproduced by the electrolysis of a solutionof tartar emetic in antimony trichloride.It consists of metallic antimony mixedwith from. 4 to 12 per cent. of antimonytrichloride.

Amorphous antimony is unstable, andwill return to the more usual crystallineform of antimony with explosive violencewhen merely scratched or given a slightblow. On this account, it is often knownas " explosive antimony."

(To be continued)


The Kiel Canal in Peace Time

In Kiel Bay.

IN peace time the Kiel Canalwas a very important en-gineering achievement

worthy of comparison in size,but not in usefulness, with suchgreat ship canals as Suez andPanama. When war broke outit was instantly transformed intoa strategic waterway of theutmost importance. During theGreat War it almost doubledthe strength of the so-calledGerman " High Seas " Fleet, byoffering a safe refuge with exitson two seas. Our cartoonistsdubbed it the " Kiel Kennel "and 15ved to picture it as an elongated funk -hole in which a frightened daschund wascowering. It is highly probable that itwill assume still greater importance in thepresent struggle.

It is very significant that the Germansdid not begin the Great War until thewidening and deepening of this canal hadbeen completed. The dates are veryimportant. The canal was first built duringthe years 1887 to 1895, but when completedwould only accommodate small craft,When the Kaiser planned to attack us, hefirst decided to widen and deepen thecanal, and replace all low bridges by loftyviaducts 131 to 140 feet above the water,or by swing -bridges. This work wasfinished by June 1914, and Germanystarted the War in August !

Small CraftIt is interesting to observe that the small

commercial canal as first constructed wasamply large enough to accommodate allthe ships which desired to use it, and costonly £7,800,000, but widening and deepen-ing it for battleships cost over elevenmillions more. Actually more than half thecommercial ships using the canal are smallcoasting craft of four hundred tons andunder. Big ships cannot afford to use itat all because the saving in distance byusing the canal is so slight. The greatestsaving on any voyage is from Hamburgto Bornholm, which is 250 miles by canal,and 610 by going round the Skaw, a matterof only 46 hours longer. As compared with

Coming out of Brunsbuttel Lock into the canal

By G. Long, F.R.G.S.this the Suez Canal shortens the journeyfrom England to India by six thousandmiles. The Panama Canal shows even morestriking results. The voyage from NewYork to San Francisco is shortened by5,262 miles, and from New York toGuayaquil by 7,405 miles. Some othercomparisons may be of interest. The KielCanal is 61 miles in length. Panama is 42,and Suez 104. The locks on the KielCanal are 1,082 feet long, as against 1,000at Panama. They are said to be thelargest in the world, and this for a canalwhose legitimate commercial traffic consistsof small coasting craft under four hundredtons !

A Simple JobThe Kiel Canal was cheaper to build

than the others, because the job was asimple matter of digging a ditch at sea -level through soft soil-not rock as atPanama, with a lofty mountain ridge tocut through.

The cost of the original Kiel Canal was£125,300 per mile, Suez cost £245,785 amile, and Manchester £516,547. ThePanama Canal was very expensive, thetotal cost being $539,200,000, which at theprogent rate of exchange is about onehundred and thirty millions sterling.

As against this the Suez and PanamaCanals, by saving shipmasters thousands ofmiles, are able to charge large tolls, butKiel can only exact small dues, and isunable to increase them, or to pay ,its way.

From an engineering and mechanical

The great lock, Brunsbuttel

standpoint a voyage through thencanal is very interesting.

When sailing there fromEngland I entered the canal atthe western entrance. This isBrunsbuttel. Harbour with fourhuge locks, in one of whichour small steamer seemed com-pletely lost like a doll in a swim-ming -pool. The locks arenecessary because there is avariation in tide level at thewest end of ten feet, but as theBaltic is practically tideless themaximum variation there isonly 1.7 feet, and this is due towind. It is thought that if ourgallant airmen could destroy thelock gates at both ends just

before a high tide with a western gale, thereis a chance that the rush of water throughthe canal might sweep the whole GermanFleet out of its funk -hole once and for all.The Canal Approach

The approach to the canal is through thenarrow channel of the River Elbe for fifteenmiles, which makes the Canal safe fromnaval attack. The shores are flat andmuddy, and the waterway is protected bylow earth banks. About four miles fromBrunsbuttel we passed under the first ofseveral remarkable high level bridges whichvary between 130 and 140 feet above surfacelevel. At nineteen miles we passed underthe Grumental high level bridge whichcarries the road, and a single line of railwayacross the canal at a dizzy height. Duringthe whole voyage we scarcely saw a ship,but a few motor boats and sailing yachtswere encountered, and they-like the cyclistson the road beside the canal-all carriedswastika flags.

Five so-called sidings were passed, theseare deep widenings of the canal, where twobig ships could pass, but were really madefor the German battleships to hide awayfrom Admiral Beatty.

At forty miles we entered Audorf lake,which is used as a turning -place for ships.This is the first of a chain of small lakeswhich extend for about five miles. Thecountry now is more undulating and thecut of the canal passes through a numberof low hills which are much prettier thanthe mudflats and marshes previously


encountered. At Levensau we passedunder another high level bridge, whichcarries a single line of railway, and a road.Three miles more brought us to the Balticexit of the canal at Holtenau, and afterpassing through the mighty locks we sailedinto the sparkling waters of Kiel Bay.The whole voyage took about twelve hours,as steamers are not allowed to travel fastin case of damaging the canal banks by thewash from their propellers.

Remarkable FactsThe building of the Kiel Canal links up

with some remarkable facts in Germanhistory. The German militarists had longplanned its construction, as a checkmate-as they believed-to the British navy.But two things stood in their way, firstlythe line of the canal must pass throughDenmark, and secondly the western outletwas commanded by the-then-Britishisland of Heligoland. These difficulties

were surmounted in typical Hitler fashion.In 1864 Prussia, in alliance with Austria,made an unprovoked attack on peacefullittle Denmark, and stole the southernportion of the country. Two years laterthe robbers quarrelled and Prussia foughtAustria, but that is another story. Thereremained the problem of British Heligo-land, whose red rocks rise from the sealike a miniature Gibraltar opposite the-approach to the Kiel Canal.

A New Pattern -Making nethod

Fig. 1.-The moulded pattern made in plasticine

WH EN a number of small parts ofsomewhat intricate design have tobe cast in any non-ferrous alloy,

as is often the case in model making and insmall light mechanical arid engineering jobs,it becomes necessary to snake a pattern. Itis advisable that the pattern should be asexact as possible in order to facilitatemachining, and in order to give a goodappearance to the finished model or machine.

The maldrig of small wooden models isdelicate and a tedious process. The methodhere to be described avoids the troublesconnected with such small wood working,and enables awkward shapes to be madeeasily and quickly ready for the foundrymoulders. The plan is to use plasticine-the clay -moulding compound.

The part is fashioned with the plasticineto the size and shape of the finished article,and is allowed to dry thoroughly. Thisclay " pattern .",(to use the founder's term) -could be used directly to make the sandmould in the foundry, but it would notwithstand continued use. It would be frac-tious and would also bend and become dis-torted with the ramming, and probablycould only be used for one casting. Toovercome this difficulty the plasticinepattern is used to make a plaster of parismould, from which is easily cast a leadreplica of the plasticine pattern, and thislead replica can be used as the pattern tobe sent to the foundry and from which anyamount of other pieces may be mouldedand cast in the metal intended for the job.The Pattern

In Fig.' 1 we have a supposititious case,which shows the pattern moulded in plasti-cine. A box (it may be of cardboard) isfilled to the -level of the top with soft plasterof paris, and the plasticine pattern is laidin it while soft to a depth which will bringthe plaster to a level a little higher than halfof the depth of the pattern. The plaster isthen, when nearly set, carefully scraped

CL AY PATTERN

_1 Simple Method of Making SmallJlodels ivith Plasticine as the Mould-

making Compound

away so that its upper surface is level withthe top of the box and half the height of theplasticine pattern, as shown in Fig. 2, andthe plaster is allowed to set hard and thepattern lifted out.

The mould is next taken from the card=board surround, carefully so that the latteris not injured, and at each side and at eachend a slanting half -circular groove is cutdown from the top surface as shown inFig. 3. The top surface (which will bethe parting surface) and the four slantingside grooves are varnished with a shellac

Fig. 3.-(Above) Details

of the half -circular groovescut in the mould

Fig. 2.-(Left) The Pat-tern embedded inplaster of parts

Fig. 4.-(Left) The card-board box isreplaced on the

plaster block

spirit varnish which dr'es quickly. Thecardboard box is now replaced on theplaster block so that it reaches high upabove the surface (Fig. 4). The plasti-cine pattern is carefully replaced in themould shape it has made and the wholeremaining space is filled with fairly liquidplaster and allowed to set.

Two Halves of the MouldWhen hard, the surrounding cardboard

box is removed and we have a plaster mouldin two halves which will produce the originalshape. The slanting grooves at the sideswill have formed corresponding projectionson the top block of the plaster. All thatremains is carefully to drive (from theinside to prevent the drill breaking throughinto the mould) a runner hole for pouringthe lead, and two vent holes to allow thegases to escape and ensure the lead fillingthe mould.

We now have a plaster of paris double,mould (Fig. 5) with side lugs which locatethe two halves accurately in position, andcan weight down the top half, or clamp itwith a clamp, and pour the lead in to forma strong lead pattern, an exact replica ofthe plasticine model, and can obtain as manyas desired and send them to the foundryfor casting the part we want, in any metaldesired.

The lead pattern will stand up to thefoundryman's handling, and since we cansupply several and easily cast new ones ifthey get damaged or out of shape, we havea means of getting as many castings as wewant, while the supplying of several pat-terns to the foundry facilitates workenormously when a good many of the sunepieces are required, for the. plaster mouldremains intact. The same procedure canof course be followed whatever the firstpattern is made of, and since the wood is attimes awkward because of its grain makingit friable in small intricate pieces it is oftenan advantage to cut out a rough woodenmodel with no great accuracy but of amplesize. It can be used in the manner shown toget a lead casting. The lead casting shouldnext be trimmed with files, etc., and used asa pattern for the foundry or as a patternfrom which to make another plaster mouldas described. Thus several patterns can bemade at little extra work and expense.

VENT FILLING HOLE

Fig. 5.-Thedouble mould


Chemistry for BeginnersNo. 8.-The Chemistry of Copper.Interesting and Simply -made CopperCompounds which can be inexpensivelyProduced in any Home Laboratory

NEXT to iron, copper is, perhaps, themost valuable metal which wepossess. It has also the distinction

of being one of the oldest metals known tomankind. As an electrical conductor,copper is, next to silver, the most efficientof all metals. In order, however, that itsconducting properties be not impaired, it isnecessary for the copper used for electricalpurposes to be of the highest .degree ofpurity. Fortunately, by electrolyticalmethods of production, it is not difficultcommercially to obtain metallic coppercontaining as little as 0.2 per cent. ofimpurity. Such " electrolytic copper," asit is termed, is nowadays employed for allelectrical purposes. Hence, by using piecesof scrap copper wire for the experimentsdescribed in this article, the amateurchemist can prepare salts and otherderivatives of copper which are almostperfectly pure.An Interesting Metal

From the standpoint of the amateurchemical worker, copper is an extremelyinteresting metal, and many easily preparedcompounds are to be obtained from it.Many copper compounds, also, areextremely useful substances. Copper

crystallise satisfactorily. It is, however,quite a simple matter to evaporate thecopper nitrate solution carefully to drynessand thus to obtain the salt in a non -crystallised condition.

Copper nitrate is a very interesting salt.A 10 per cent. solution of it in water

Practical Experiments for theHome Worker

sulphate, for instance, is a well-knownfungicide, entering into the composition ofcountless horticultural compounds. Othercopper compounds are employed in photog-raphy. Others, again, are used as pigments,whilst, through the agency of one coppercompound, artificial silk becomes possible.

In our preparation of a series of interest-ing copper derivatives, let us. start with oneof the simplest of these compounds. Obtaina few pieces of copper wire, cut it up intoshort lengths and place the pieces in anopen -necked bottle. Add just sufficientwater to cover the copper wire and thenpour into the bottle a few drops of nitricacid. Immediately a chemical reaction willtake place. The copper and the nitric acidwill interact, giving rise to reddish fumes-oxides of nitrogen-which will escape fromthe bottle, and a brilliant blue solution ofcopper nitrate will be formed. When theaction ceases, add a further quantity ofnitric acid and keep adding the acid little bylittle until all or nearly all the copper hasdissolved.

Now pour the blue solution into a cleanevaporating basin and heat it with a bunsenburner or spirit lamp or by immersing thebasin in a pan containing boiling water untila thick syrupy blue liquid remains. Thenput the flask or basin aside to cool.Copper Nitrate Crystals

If you are lucky, long crystals of coppernitrate will separate out after a time, butcopper nitrate is a difficult substance to

provides a blue light -filter used sometimesby microscopists and photographers forpassing blue light only. Copper nitrate is,also, a powerful oxidising agent. If, forinstance, a piece of blotting paper be

Canvas soaked in a solution of copper sulphateis rendered rot and mould proof.

The apparatus for pre-paring copper powderby passing hydrogen gasover heated copper oxide.

saturated with a strong solution of coppernitrate and then warmed by holding it infront of a fire, the paper will often ignitespontaneously owing to the oxidisingpowers of the nitrate. Similarly, if a fewpieces of copper nitrate be quickly wrappedup in tin -foil, the latter will rapidly becomeexceedingly hot and, often enough, willburst into flame, the tin -foil becomingconverted into white tin oxide.

From copper nitrate to copper oxide is avery simple step. The copper nitrate ismerely heated, either in a porcelain crucibleor in an old can or other suitable container.When strongly heated in this manner, thecopper nitrate will give off red oxides ofnitrogen-by the way, these fumes arefairly poisonous and should not be breathed-and a black residue of copper oxide willremain.Well-known Oxides

There are two well-known oxides ofcopper, cupric oxide, CuO, which is blackand which is prepared as above, andcuprous oxide, Cu2O, a red powder, which isusually made by adding grape sugar to analkaline solution of a copper salt. Onheating, red cuprous oxide will be pre-cipitated. The same red copper oxide canalso be made by gently heating a mixtureof sodium carbonate and cuprous chloride.

To return, however, to the more commonblack copper oxide. This is a most usefulsubstance to have, for, using it as a startingpoint, a number of pure copper compoundscan be prepared without difficulty.

For instance, the well-known coppersulphate is readily prepared in a state ofhigh purity by dissolving black copperoxide in warm dilute sulphuric acid and byevaporating the resulting blue liquor downto crystallising point. Many amateursendeavour to make copper sulphate bydissolving metallic copper in strong sul-phuric acid. This, however, is not a goodmethod. For one thing, choking fumes ofsulphur dioxide are given off, and, again,copper is only soluble in hot concentratedsulphuric acid, forming a mixture of coppersulphate and copper sulphide, the latter ofwhich is black and whose separation from


the hot concentrated acid -by filtration isdifficult.

Crystallised copper sulphate, CuSO4.5H20possesses a beautiful blue colour. If, how-ever, the crystallised copper sulphate isheated just above the boiling point of waterfor some time, the salt loses four of itsloosely attached water molecules and itbecomes converted into a pale bluish -whitesulphate having the formula, CuSO4.H20.If crystallised copper sulphate is heatedmore strongly, say at a temperature of250 deg. C., it becomes converted into anhydrous (or water -free) copper sulphate,CuSO4, which is a perfectly white powder.

Water DetectorAnhydrous copper sulphate is much used

in chemistry for detecting the presence ofwater. Exposed to the air, it quicklyabsorbs water and turns blue. Added toliquids such as alcohol, benzene, petrol,the anhydrous copper sulphate will indicatethe presence of the slightest trace ofcontained water by undergoing its remark-able colour -change from white to blue.

It is easily possible to obtain metalliccopper from a solution of copper sulphate.If, for instance, a steel blade br an iron nailbe plunged into a solution of copper sulphatethe blade or nail will quickly becomecovered with a layer of red metallic copperwhich can generally he scraped away veryreadily. The solution can also be used forelectro-plating. The article to be platedforms the negative electrode of the cell, anda bare piece of copper wire the positiveelectrode. Connect a flashlamp batterybetween the two electrodes and copper willimmediately begin to be deposited on thearticle to be plated.

Copper sulphate solution is a powerfulanti -fungus and anti -rot compound. Soakwood, canvas or other fabric in moderatelystrong copper sulphate solution and thenallow it to dry out. Such material will thenhave high rot -resisting and anti -mouldproperties imparted to it.

If to a solution of copper sulphate orcopper nitrate, or, in fact, to any solublesalt of copper a solution of sodium hydroxide(caustic soda) is added, a pale blue pre-cipitate of copper hydroxide, Cu(OH)2,will be formed. It will be advisable for thechemistry enthusiast to prepare a quantityof this copper hydroxide, because, bydissolving it in organic acids, as, for examplecitric, tartaric or acetic acid, the copper saltsof such acids can be prepared withouttrouble. When adding sodium hydroxidesolution to the solution of copper sulphateor nitrate in order to prepare copperhydroxide, only add the least possiblequantity of the sodium hydroxide solutionto effect complete precipitation of thecopper hydroxide. If more sodiumhydroxide solution is added, it will con-taminate the precipitated copper hydroxideand will prove difficult to wash out com-pletely when the copper hydroxide iscollected by filtration.Copper Carbonate

When copper hydroxide, Cu(OH)2, isboiled with water it turns black, becomingconverted into a compound having thesupposed composition, Cu(OH)9.2CuO.

If, instead of adding sodium hydroxide(caustic soda) solution to a soluble coppersalt, a solution of sodium carbonate is addedcopper carbonate will be precipitated. Thisis a greenish -blue insoluble compoundhaving, usually, when prepared in thismanner, the composition, CuCO3.Cu(OH)2.Like copper hydroxide, copper carbonateis completely soluble in acids, and, whendissolving, it evolves carbon dioxide gas.

A form of copper carbonate constitutes

the well-known greenish mineral, malachite.Artificial crystals of malachite can be madeby immersing a flat piece of limestone in amoderately dilute solution of copper nitrateuntil the limestone is covered with a greenlayer and then by immersing it for a fewdays in a solution of sodium carbonate(or common soda) of similar strength. .

Copper carbonate is also known asverdigris, and, it is very slowly formed on thesurface of metallic copper when the metalis exposed for prolonged periods to moist aircontaining considerable quantities of carbondioxide.

Soluble in AcidsCopper carbonate and copper hydroxide,

as we have noted, are completely soluble inacids with the formation of salts. If, forinstance, we desire to make a quantity of.say, copper tartrate, all we have to do is topour some strong tartaric acid solution intoa flask and then tn_ add either copperhydroxide or copper carbonate a little at atime. The hydroxide or carbonate willdissolve completely (in the latter instance.with much effervescence and evolution ofcarbon dioxide gas) and a bluish -green

otherwifie the black copper sulphide, CuS(cupric sulphide), will be formed.Schweitzer's Reagent

One of the most interesting of all coppercompounds is that which is known asSchweitzer's reagent. This consists of asolution of copper hydroxide, Cu(OH)2, inammonia. It has the remarkable property ofdissolving paper or cellulose. It is mostconveniently prepared by adding ammoniadrop by drop to a strong solution of coppersulphate contained in a flask. The character-istic pale -blue precipitate of copperhydroxide will be formed. After theprecipitation of the copper hydroxide ceases,the addition of the ammonia is continued.The liquid will then acquire a rick dark -

blue coloration, due to the solution of thecopper hydroxide in the excess ammonia.At this stage, the flask should be shakencontinuously, the ammonia being addeddrop by drop. When the last of theprecipitated copper hydroxide dissolves,add a few drops more of ammonia and thepreparation of Schweitzer's reagent willthen be complete. Cotton wool and goodquality filter or blotting paper will dissolve

Preparing metallic copper in powder form by passing hydrogen gas over healed copperoxide

solution of copper tartrate will result. Thecopper hydroxide or carbonate is added tothe tartaric acid solution until all actionstops and until it ceases to be dissolved.The resulting solution of copper tartrate isthen poured off and crystallised by evapora-tion. Copper acetate and copper citrate aremade in the same manner, employingsolutions of acetic and citric acids respec-tively.

If to a solution of any salt of copper weadd a quantity' of waterglass (sodiumsilicate) solution, a beautiful greenishfibrous precipitate of copper silicate will beobtained. Copper silicate is a most enduringsdbstance. It occurs in mineral form asEmerald Copper and as Chrysocilla.

In a similar manner, if sulphurettedhydrogen gas or a solution of ammoniumsulphide be added to a solution of a coppersalt, black copper sulphide, CuS, will beprecipitated. This is insoluble in water, butdissolves in mineral acids with the evolutionof the evil -smelling sulphuretted hydrogengas.

Another form of copper sulphide havingthe formula, CIO (cuprous sulphide), isformed as a grey -looking mass when copperfilings are heated with sulphur. The copperfilings must be in excess over the sulphur,

in the blue liquid and, on the addition of adilute acid, will be re -precipitated in agelatinous form. Such a chemical reactionforms the basis of one of the methods ofartificial silk production.

The deep -blue colour of the above liquidis due to the formation of copper ammoniumsulphate. If methylated spirit is added tothe deep -blue liquid and the latter allowedto stand for a few hours, deep violet -bluecrystals of copper ammonium sulphate willbe formed. These can be filtered off, washedwith water containing ammonia (not withpure water, for they would dissolve in this)and -then preserved in a hermetically -sealedtube. The crystals of copper ammoniumsulphate cannot be preserved otherwise, for,in contact with air, they slowly give offtheir ammonia and change back again intocopper sulphate.

Metallic CopperMetallic copper is not satisfactorily

soluble in hydrochloric acid. Therefore,copper chloride cannot be prepared- bydissolving the metal in the acid. Copperoxide, hydroxide and carbonate are all verysoluble in dilute hydrochloric acid, a deepgreen solution of cupric chloride beingproduced. Copper (cupric) chloride has the


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NAME Age

ADDRESSICS


-4*

INTERESTING WORKfor WINTER EVENINGS

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We invite old friendsof the past andyounger friends of:he future to get acopy of this New"London Opinion"and to judge forthemselves whetherit is worthy of theirsupport.

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chemical formula, CuC12. It can becrystallised from water, the crystals havingthe composition, CuC12.2H20. Whencrystallised cupric chloride is stronglyheated, it gives off chlorine gas and isconverted into cuprous chloride, Cu2C2,which is another well-known chloride ofcopper.

The terms cuprous and cupric are appliedto copper compounds to denote theirchemical composition. Copper forms twodistinct series of compounds, to which thenames cuprous and cupric are given. Thus,as we have already seen, there is a cuprousoxide and a cupric oxide, a cuprous chlorideand a cupric chloride, and so on.

whereupon the cuprous chloride will beprecipitated as a white powder.

Cuprous chloride is soluble in hydro-chloric acid, ammonia, sal -ammoniac andcommon salt solutions, but its solution inany of these liquids cannot be kept for long,except in a hermetically -sealed tube. Fairlyrapidly, these solutions absorb oxygen fromthe air, first turning brown and ultimatelydepositing a greenish precipitate of copperoxychloride, CuC12.3Cu0.2H20.

Copper PowderA most interesting substance is copper

powder. This can be made by placing aquantity of copper oxide in a glass tube

CuO + 2H = _Cu -I- H2O(Copper oxide) (Hydrogen) (Copper) (Water)It is best to seal off the copper powder in

tubes if it is desired to preserve the material,for the metal in this condition does not keepvery well. Indeed, on occasions, the powdertakes fire or heats -up spontaneously whenshaken about in the air. This is due to itsrapid oxidation and its conversion intocopper oxide.

Finely divided metals which take fire inthis manner are sometimes called " pyro-phonic metals." Lead, for instance, isanother metal which can be prepared bychemical means in the pyrophoric con-dition. Iron, again, is another such metal

METALLIC COPPER(DEPOSITED)

COPPER SULPHIDE

COPPER CHLORIDE(CUPRIC)HYDROCHLORICACID ANDMETALLIC 1COPPER

COPPER HLORIDE(C UPROUS)

AIR

COPPER OXYCHLORIDE

COPPER (METALLIC)L L IC)

NITRICACID 0 tr

is* '<"'

Ct.COPPER NITRATE

ec CAUSTICSODA

D?' 111 EATWO °GE%

Po COPPER OXIDE

- pov

IHYDROGEN

Co o.

FINELY-DIV I DED-COPPER.

COPPER CARBONATE

COPPER HYDROXIDE(BLUE)

IBOILEDWITH WATER

COPPER HYDROXIDE0

(BLACK)

yJTi

OsC ?PER SULPHATE /R

COPPER SILICATE,

ry

EIEcrRHEAT

°Y.sis METALLIC COPPER(DEP05/ TEO)

COPPER SALTS

(E.G. - COPPER ACETATE,COPPER TARTRATE etc)

COPPER SULPHIDE

COPPER AMMONIUMSULPHATE

REAGENT)(SCHrVEITZERS

COPPER AMMONIUM CHLORIDE ANHYDROUS COPPER SULPHATE

Scheme showing the manner in which a number of interesting copper compounds can be made

Cuprous chloride, Cu2C12, is a compoundwhich differs widely from cupric chloride,CuC12. It is best prepared by dissolvingcrystals of cupric chloride in strong hydro-chloric acid and then by adding a quantityof clean copper wire cuttings to the liquid.The solution is now boiled until it becomescolourless or nearly so. During the boilingprocess, the hydrogen liberated as a resultof the action between the hydrochloric acidand the copper converts the cupric chlorideinto the cuprous state. After the decoloris-ation of the liquid, the contents of the flaskare poured out into a basin of cold water,

(such as a bulb -tube) and by gently warmingit, at the same time allowing a stream ofhydrogen gas (generated by the action ofzinc on dilute sulphuric or hydrochloricacid) to pass over it. Slowly, the blackcopper oxide will turn to a brick -red shade,and then to an almost golden -red hue. Thereddish material in the tube is no longercopper oxide, but is, in fact, metallic copperof an exceedingly high degree of purity.In its preparation, the hydrogen haschemically combined with the oxygen of thecopper oxide, forming water, and leaving thecopper behind :-

Copper in its powder or finely dividedform does not differ in any way chemicallyfrom metallic copper as it is commonlyknown. Perhaps, however, the finelydivided metal is rather more active. If,for instance, clean copper wire is placed in aflask and strong ammonia solution pouredon to it, the liquid will, in time, becomeblue -coloured, owing to the action of theammonia on the copper. With ordinarymetallic copper, the action of the ammoniais very slow, but, employing finely dividedcopper, the production of the blue am moniacalcopper solution proceeds much more rapidly.

A Chimney -Sweeping SetA REALLY efficient chimney -sweeping

set can be made out of three-ply at acost much below that of any marketed set.Obtain a piece of fif in. three-ply,3 ft. 6 in. or 4 ft. long, and cut a number of

TYPE OrBOLTUSeD

Details of theconstruction

2-i in. strips from it to suit your require-ments.

A 9 in. lap should be allowed, and I in.bolt holes should be drilled 1 in. from theends of the strips, the two holes being 6 in.apart. Keep the drilling standard in orderto facilitate assembly.

A circular brush, such as may be pur-chased for 6d., is secured with wire to theend of one section, and in. bolts 1 in. long(under head) are used for, coupling thestrips.

Removing ScrewCaps from BottlesTIGHT

-FITTING screw caps on bottlesand jars are often the cause of much

waste of time and sore fingers : in mostcases the grip or milling on the cap is in-sufficient to obtain a really firm hold. The

illustration shows a useful gadget whichcan very easily be made from a hardwoodcaster and a piece of rubber.

Cut out a strip of the caster so that thetwo halves form an oval when placedtogether. Next secure a strip of rubberwith rubber solution inside each half, andfinally flute the outside of the caster with agrooving chisel:

Details of thedevice -


Fig. I.-The completed engine showing the slide -valve mechanism

NEARLY fifty years ago, when I wasan apprentice in the workshops ofone of the old telephone companies,

I designed and made a model steam engineof an unusual type. Actually there was noprototype driven by steam from which tocopy and my model was made to follow thelines of a Crossley Gas Engine; the old pat-tern, of course, in which the gas admissionvalve was of the sliding form. Those were,I believe, the days before the introductionof poppet and mushroom valves. Anywaythe engine, by which I was inspired andwhich I had seen many times at work, hada flat valve. So I set to work, made mydrawings and from those the foundry pat-terns for castings.

First Serious AttemptThis was my first serious attempt at

model -engine making and I have oftenwondered how the founder managed to castmy bedplate, since I made the pattern ofexactly the same shape as the casting wasrequired to be. Actually, I should haveput a print on the cylinder end of thepattern so that the hole, which was toreceive the cylinder, could be cored out.But I knew nothing about cores and core -boxes, and I suppose the good-naturedfounder, recognising that I was but anovice, and desiring to help me, stuck along plug in the hole that I had bored in thewood and made a simple little round core toplace in the mould. Most likely he explainedto me what I should have done; I do notremember, but the result was satisfactoryfor my casting was as I wanted it.

One of the first thoughts which occurredto me, after I had tested its ability to work,was that its extreme simplicity made it anexcellent subject for a beginner in model -making, so from my youthful effort I havemade a fresh set of drawings for the use ofthe reader, and these are reproduced here.

Before making references to the drawings,I think that the reader would like to knowwhat the general appearance of the engineis, and so I have taken two photographs ofit, which are reproduced here in Figs. 1 and2. They both show the slide -valve side ofthe engine, but are taken from oppositeangles.

Uniflow PrincipleI do not know whether my reader is

familiar with the term " uniflow " in con-nection with steam cylinders. If he is he

will know that some engines have valves ofsuch a type and design that the steamalways flows in one direction throughvalves and ports ; that is to say, steam whichhas done its work of driving the piston isexhausted back through a different portfrom that through which it entered. Theobject of this arrangement is to avoid the

M OD ELwould be connected to the boiler; the upperis the exhaust. Both of these are in straightlines with ports in the valve cover -plate,in the valve and in the block on the cylinder.Steam enters through the bottom port anddoes its work in driving the piston from oneend of the cylinder to the other ; in themeantime the valve is moved by a smallcrank and this expanded or exhaustedsteam then passes out through the upperand somewhat larger pert to the atmo-sphere.

Single -ActingThe simplicity of the engine lies in the

fact that it is single -acting. Steam drivesthe piston in one direction only and theweight and momentum of the flywheel isdepended upon to return it ready for anotherpower impulse.

Obviously, size for size, such an engine isnot so powerful, but it is easier to make alarger single -acting cylinder and valve thanit is to make one of half the size which isdouble-acting, closed at both ends, for suchclosing at the end towards the crankshaftinvolves a stuffing box to make a steam -tight joint around a piston rod, a crossheadand its guides between the piston rod andthe connecting rod, and a closed steamchest to contain the slide valve, which

The Simplicity of this Engine Lies in the Fact that it is Single -

acting. Steam drives the piston in one Direction Only andthe Weight and Momentum of the Flywheel Returns it.

cooling of the live steam passages by thelower temperature of the expanded steam.Now I do not anticipate for a moment thatI knew at the time what I was doing, but Ithink it likely that my little model musthave been one of the earliest to work on theuniflow principle.

An examination of the photographs willshow that there are two pipes leading to theslide valve ; one, the lower, is that which

CA Le .7..t.,.°or VICHE>

/3/4

chest must have another stuffing box arounda valve rod.

Turning to actual construction anddetailed dimensions, I do not think thatmuch need be said regarding these, for Ihave endeavoured to make descriptionunnecessary by completeness in the draw-ings, of which Fig. 3 is a side elevation, Fig.4 a plan of the whole engine, and Fig. 5 adrawing, the main object of which is to

4y4'Fig. 3.-A side elevation


HORIZO NTAgive the reader exact measurements for allradii in setting out the spokes and otherdetails of the flywheel when making thefoundry pattern.The Bedplate Pattern

When the bedplate pattern is taken inhand, do not forget that either the cylinder

By E. W Twining

end should be left solid, to be drilled andbored out to take the tube of the cylinderwhen the casting is received, or a print puton the pattern of the correct diameter sothat the foundry -man can make a core ofthe same size to drop into the mould in theimpression left by your print. A core -boxwill not be needed ; he can make a cylin-drical core without a box by ramming thecore sand in a piece of tube.

The flywheel should be cast in soft ironwhich is easy to machine, but the bedplatemust be in gunmetal because the cylinderis to be soldered in by sweating with abunsen flame.

The cylinder is made from a piece ofthick seamless brass tube whia will dis-pense with the necessity for boring it out inthe lathe ; indeed, were it not for the piston,the cylinder cover and the turning of theflywheel, this model could be made withouta lathe. It will be advisable to lap the insideof the cylinder, after it is soldered in the

in order to ensure that it is trueand smooth and a good fit around the pistonwhich may also be lapped into the cylinderafter it is turned. The preliminary lap canbe of wood, beech preferably, turned quitetrue and a nice sliding fit in the tube. Smearthe lap with a little of the finest emerypowder in oil and work this backwards andforwards with a circular or twisting motionuntil you see the whole inner surface of thetube bright, then wash the cylinder inparaffin and, if possible, leave it, placedvertically in paraffin for a few days whilstsome other part of the engine is being made.Lapping may then be completed by usingthe piston itself, the abrasive being a finemetal polish such as " Brasso." Wash this

SCALEcw INCHES

2

L ST EAM NG11

Fig. 2.-Another view of the slide -valve mechanism

away with paraffin in the same manner.Hollow Piston

As will be inferred from Figs. 3 and 4the piston is hollow, of the " trunk " type ;it can, being quite small, be turned from apiece of in. diameter brass rod. It has onegroove to be filled with soft'cotton packing. The crankshaft is of steel and is built upas shown in Fig. 4. The jointscan, if it is so desired, bemade by brazing instead ofriveting and in fact this will,if facilities are available fordoing it, make the better job,but it involves making asplit big -end on the connect-ing rod ; my own little crankswere not brazed, but the websdrilled so that the shaft andcrank pin were a good drivingfit, and the ends -were justlightly riveted over. Theflywheel also was a knock -onfit, the shaft being very slightlytapered with a dead smoothfile in the lathe.

t

.1

I

2

Fig. 4.-A plan view

NE

The cylinder cover is soldered in at thesame time as the valve -face block. Thelittle disc crank which serves as an eccentrici ; knocked on to the shaft end and made

DIAMETGR 3%2*

Fig. 5.-Details of the flywheel

fast by drilling and screwing in the pinwhich drives the valve rod.The Valve Block

Details and measurements of the valveblock or port face and cover plate will beclear from the drawings, particularly fromFig. 6, and I think it only necessary tomention two things ; first that the nuts ontwo of the four studs may be placed oneither diagonal and must be adjusted sothat the valve is pressed well up to bothworking faces but not too tightly; second,that the steam and exhaust pipes aresoldered into the cover plate and the steampipe will need a union between the engineand the boiler, preferably close to the coverplate.


.1%r

SLIDE -

VALVE

THICKtIESSYit VICK/--r-

exhIAU,Tpint

N

STEAM NOE-.

%CYLI/1DiR PORT FACE VALVE COVER PLATE

Fig. 6.-The valve block and cover plate

The cycle of operations in one revolutionof the crank shaft, or as they are technicallytermed-the valve events-are set out inthe diagram Fig. 7, where at A the pistonhas nearly completed its exhaust or forwardstroke and the valve is just commencing toopen the steam ports. B shows the steamport fully open with the piston nearly mid-way in the power stroke whilst at C thestroke is almost completed and the porthas just closed.

In sketches D and E the exhaust port Eis shown, where at D the port is just aboutto open and at E has just closed. An inter-mediate sketch would, of course, haveshown the crank in the position diametri-cally opposite to that at B and the exhaustport fully open. Other reference letters inFig. 7 are : V, the valve, P, the piston, MC,the main crank pin, and EC, the eccentriccrank. The arrows, of course, everywhere,indicate the direction of movement : of thesteam, of the exhaust, of the valve and ofthe crank shaft.

1-4- 5A6" -4-1

The PulleyMy own engine has no pulley upon

the crank shaft but in the plan Fig. 4I have drawn the shaft long enough,beyond the flywheel, to take suchpulley, which the reader can add if hethinks fit. Pulleys can be made bycasting from a pattern, or built up. Ihave shown the latter method becauseit will result in a lighter and neaterjob. The hub is turned from a piece ofbrass rod, the spokes are formed froma disc of brass plate, perforated andsweated with solder on the hub andthe rim from a piece of lb -in. diametersteel bicycle tubing also soldered.

I have only dealt withand drawn the modelexactly as I made it,years ago, but I stronglyrecommend the readernot to copy the diminu-tive size but to make hisengine twice as large asmine ; he will then havea model which is not

only more imposing to lookat but which will be useful fordriving other models of machinetools, etc. This he can., quiteeasily do by doubling every oneof the dimensions given inFigs. 3 to 6. But it will bevery advisable to put -it littlemore detail into one or two ofthe working parts. Thus theconnecting rod big -end hadbetter be in two parts, madeof gunmetal, both separatefrom the rod, and the mainbearings be fitted with brasses.

Changes RecommendedThese alterations will ne-

cessitate a little modificationin the main crank measure-ments. Fig. 8 shows thewhole of the changes involved,or recommended, in making' he larger model and it should

÷-716""

I;,

illSgr/U11111Q: Y

portions as drawn in Fig. 8. The valve rodalso of steel is rectangular in cross section ;it can be filed up from a bit of strip andcurved as shown in the plan Fig. 4. There isno need to fit brass ends to this.

The base or block on which the engineis mounted is a piece of hardwood, in mycase mahogany. To this the bedplateshould be secured with a stud and nut atthe crank end and, immediately behind thecylinder, on the centre -line, by one counter-sunk wood screw.

With regard to finish ; the rim of the fly-wheel, pulley, crank shaft, cranks, connect-ing and valve rods, should all be polishedbright as also the gunmetal big -end and

wit

/\yV

.111

/ "e '/

't:113k's

Fig. 7.-The cycle of operations in one revolution of the crank shaft

brass bearings. All the rest may beenamelled in colours to suit individual taste.On my own model the base block, the fly-wheel, the port face block and valve coverplate are black, the bedplate and cylinder abright blue-green ; as nearly as possible thecolour which these parts of the Crossleygas engines are, or used to be, painted.

Since completing this article it hasoccurred to me that a greater number ofyoung mechanics may be induced to buildthe engine if it were rendered possible forthem to obtain the few necessary castings,already made and ready for filing up andmachining; thus avoiding the necessity formaking the foundry patterns. I will, if thedemand warrants my doing so, makearrangements with a supplier; providing,of course, that the present critical war con-ditions render it possible to get the foundrywork done. Only the larger, or double -size engine will be dealt with in this way.

All inquiries should be made through theEditor.

Fig. 8.-Detailsof the connectingrod, crank, an.l

bearings

be carefully noted that in thisdrawing all figured dimensions applyonly to the double -size engine.

In both small and large models the con-necting rod is of steel. In the first it issimply sweated into the brass blocks form-ing big and little ends, but in the larger thebig end is shouldered and riveted into asteel plate which is bolted to the gunmetal


Undercarriages for ModelAircraft

Although the present trend in Model Aeroplane Construction is for large models and increased speed, thedrag of the landing gear has, in consequence, been considerably increased. Therefore, the undercart mustbe designed to overcome this drawback, and below we give a few types that have been used successfully.

TWO or three years ago, when the" slab -sided " model was universal,the undercarriage was not considered

to add very much to the drag created bythe rest of the machine.

Fig.1.-The bamboo andwire type of under-

carriage

some of the different types of landing gearthat have been used successfully. Firstthere is the bamboo and wire type, which,undoubtedly, from a point of mechanicalefficiency is one of the best ever devised.

Fig. 2.-Another type ofsprung undercart

A conventional undercart on a modernmodel, however, contributes a muchgreater proportion than before, since withthe increased Wakefield weight rules, thetrend toward more powerful models, andin consequence, higher speeds, the 'dragof the landing gear has been considerablyincreased, whilst the streamlining nowgenerally employed has kept the drag ofthe rest of the machine comparatively low.

The objects of an undercart are, ofcourse, to assist in the take -off and landingof an aircraft. Unfortunately its use inthese two functions is reduced to a hind-rance whilst the machine is_in flight.

Recently, models employing foldingairscrews have appeared, and so the onlystage in which 'the undercarriage is anessential in this type is the take -off. Theideal solution to this problem, of course,would be to use an undercart placeddirectly under the centre of gravity, whichwould automatically release itself from themodel when the latter was off the ground.No Detachable Parts

Unfortunately, we are prevented fromdoing this by the rules laid down forvarious contests, which state quite clearly :" no part of the model may becomedetached during flight." And no wonder !Were it not for this rule, modellers wouldbe designing planes that not only wouldbe releasing their undercarts, but, afterpower flight, throwing away their props,rubber motors and everything not neces-sary ! Plus a bit of fin area that wouldthen not be needed ! Our landing geartherefore, has got to " stay put." We can,though, reduce the weight and drag to aminimum by using light materials, andmaking it well streamlined, or evenretractable.

However, we must not forget in thisquest for low drag and weight that it hasto be strong enough to resist take -off andlanding forces, and so let us first examine

ROLLEDPAPERTUBE

BAMBOOSTRUT

Fig. 4.-A rigid landinggear for lightweight

models

Its aerodynamic efficiency, however, is, aswill be seen from the sketch, rather poor.

SHOCKRUBBERS

PIVOTED TOFUSELAGE

HERE

HARD/BALSA

Fig. 3.-This type of gear hasshock -absorbing qualities

Non -Streamlined ModelsFor light, non -streamlined models, this

is, of course, an excellent type to use, sinceit acts as a model undercart shotild; thatis, backward and upward. In spite of the

"AN

Y11DURALTUBES

SECUREDTO FORMER

oinECORE

Fig. 5.-This type of undercart is suitable foralmost any type of duration model

SHOCKRUBBER

BALSAAIRING

much used phrase of models " settling toa perfect three -pointer " no model, withan orthodox landing gear, ever makes athree-point landing, but, if properlyadjusted, hits the ground at its glidingangle. Therefore, the undercart will besubjected to a backward and upwardblow. There are two ways of absorbingthe impact. Either by . mounting thelanding gear rigidly, and thus allowing theshocks to be transmitted through thefuselage, or to use a sprung landing gear.In the case of the latter, the bamboo andwire undercart forms an excellent example.

Another type of sprung undercart isshown in Fig. 2. This is a little betteraerodynamically, than the previous typementioned, but is usually a trifle heavier,since it has to be braced to the fuselage toprevent tearing out on extra hard landings.

The type shown in Fig. 3 has good shockabsorbing qualities, and generally looksbetter than most other types, since it tendsto disguise that " lankiness " getrerallyassociated with duration models. Itsaerodynamical faults lie, not so much inhead resistance, as in its effect on direc-tional and lateral stability. The large sidearea of the struts tend to draw the centreof lateral area forward and downwardof the centre of gravity, thus making alarge and higher fin necessary.Rigid Landing Gears

For rigid landing gears, the type shownin Fig. 4 that has been' used for sometime on lightweight models is one of thebest.

This is the ordinary single -leg bambootype, plugged into paper tubes. It hassome distinct 'advantages, which accountfor its popularity for contest models. It islight in weight, has a reasonably low drag,and in competition models, where dur-ability is not a governing factor, itsstrength is quite sufficient. Also, it fssimple to construct, and being easilydetachable, facilitates transport. Thestruts should, of course, be a little weak, inorder that they may break first in a verybad knock,instead ofdamaging thefuselage.

Thoughtypical ofthe types ingeneral use,none of thefour under -carts men-tioned areideally suitedto a highlystreamlinedmodel, andso we mustdevise one ortwo types tomeet our re- i Fig. 6.-An undercartquirements. which is light in weightIn Fig. 5 and low in drag

TAPERED

BAMBOOSTRUT


an undercarriage which should be suit-able, not only to streamlined jobs, but foralmost any type of duration model, isshown. It acts on the same principle as thelanding gears in Figs. 1 and 3, and is con-structed mainly from a single piece of steelwire (about 18 s.w.g. for Wakefield models).

The exposed length of wire is encasedin balsa, to prevent it from b'hnding and to '

preserve a good streamlined section. Ifthe shock -rubber is made detachable atone end, it will be possible to fold the strutsalong the fuselage. Thia type of undercarthas all the shock absorbing qualities of thebamboo and wire type, plus ,low drag andfairly light weight.

Another landing -gear which is light inweight and has low drag is shown inFig. 6. This type has been used on amonocoque Wakefield machine with satis-factory results, even though no form ofspringing (other than that of the bambooitself) is used. The bamboo struts aredetachable and plug into tubes. Thesetubes are hollowed and shaped. from balsablocks, which are firmly bound andcemented to the bulkhead, this beingbraced with a strip of hard balsa from theapex of the tubes to the former in front.Wheels

The wheels used on this undercart maybe of interest to readers. They are madefrom four laminations of j in. balsa,'grain crossing, and turned to an ellipticalcross-section. One outer lamination is thendetached, and firmly glued and faired tothe end of the strut, so that the axlepierces the exact centre About a quarterof an inch of is in. birch dowel, drilled,and lined with duralumin tube, is thenslid on to the axle, and the end of thelatter bent up or a small washer solderedon. The remaining three laminations arethen drilled so as to form a tight fit overthe dowel, the end of the hole being cappedor filled -in with a small disc of balsa.

The finished wheel is light in weight, yetquite strong, and the bearings will notwear loose, also it has a pleasing stream-lined appearance and adds little drag.

If a folding prop. is used, the weight anddrag of this landing gear can be evenfurther reduced, since it can then be placedat a point farther from the nose andshorter strut used.The Retractable Undercarriage

A retractable chassis is no advantageunless it c be made as 'ight as a fixedtype, since the extra performance to begained in reduced drag, will be lost inadded weight. Another point to rememberis that the centre of drag (and centre ofgravity in most types) is changed uponretraction. These two latter disadvantagesdo not have a serious effect, however, ifthe landing gear can be made to retractdirectly the model is off the ground, andbefore it has assumed a climbing angle.

The only way of enstiring a correctlytimed retraction, it seems, is to use amechanically controlled releasing -gear offthe propshaft. From my experience, landinggears which are merely kept extended bythe weight of the machine against thetension of a rubber band or spring are neververy satisfactory. Should the model bethrown momentarily off the ground (by agust of wind or irregularity in the take offsurface) before it has gained sufficientspeed to become air -borne, the under-carriage will probably retract with disas-trous results.

Unfortunately, mechanisms for operatinga retractable gear, usually add considerableweight. However, for those who feeldisposed to experiment, we show in Fig.

TUBE "

TUBE "E"

WIRE

7 a complete layout for a mechanicallycontrolled undercart suitable for Wakefieldtype models, which should not add muchweight, although, in fairness to the reader,it should be mentioned that we have not triedout this particular mechanism in practice.The Propeller Shaft

Nevertheless, the design is quite simpleand so no serious snags, are likely to beencountered. The propshaft thread shouldhave as fine a pitch as possible. A coarsepitch will necessitate a very long shaft,especially on models with a slew take -off.The nut should be easy running on theshaft, and must be securely soldered to thewire guide C, which is of 2(1 s.w.g. steelwire. The guide should be an easy slidingfit in the duralumin tube F, and in wireloop D.

Tube E is of dural or aluminium, andmust be braced firmly in all directions. It

1

v'Sf

4.Nogpt

THkEAD FROMEACH STRUTTO WIRE " D"

STOPNUT

extended position (this may easily beeffected by slipping a piece of wire throughwire D in place of guide C) and the modelmade to rise off ground. With the aid of astop -watch, the time between the momentof release, and when the model is in thecorrect altitude for retraction of the landinggear, is then noted.Weighted Tail

The only trouble likely to be experiencedhere is in the fact that the adjustmentsmade with the undercarriage up are notlikely to have the same result when theundercarriage is down, since the centre ofgravity will be farther forward and thecentre of drag lower. It should be advisable,therefore, to add a little weight to the tailtemporarily, until the model assumes a goodglide again upon being hand launched.Having found the approximate take -offtime of the model, the release mechanism is

GUIDE "C"

BALSABRACES

should be of large enough bore, whenflattened to allow wire D to slip througheasily. .The operation is as follows. Thenut is first wound right up to its stop. Then,as the airscrew shaft rotates under thepower of the rubber motor, the nut movesbackward and withdraws the wire guidefrom tube F and finally from wire D. Thestruts are then released and will swing upinto their recesses under the pull of theretracting rubber.

The nut will now have reached or be nearto the end of the shaft, and with the a Ili&C will then commence to revolve.

Test flying a model fitted with this typeof undercart, will call for a slightly differentprocedure from that normally employedwhen testing a conventional model. Themachine should first be hand launched withthe landing gear retracted. All trimmingto get maximum climb and glide should bemade, and the various adjustments noted.

The undercart should then be fixed in the

FOR.MER_

WIRE AND TUBEHINGE

B

RECESS

RETRACTINGRUBBER

1r:7zrz-1

TINPLATE STRIPSOLDERED TOBRASS TUBE &BOUND TO STRUT

BAMBOO STRIP-BETWEEN "A ft, -6

Fig. 7.-A completelayout fora mechanicallycontrolled undercartsuitable for Wakefield

type models

then adjusted to retract the chassis afterthe correct period.

With the adjustments found best duringthe hand launched flights, and the under -cart set to retract after the given time, themodel is then allowed to R. 0. G.

It is now possible that the model willtake -off slightly quicker, thus making itnecessary to adjust the release gear tooperate a little earlier (this is easily accomp-lished by slightly shortening the horizontalportion of guide C).

In the construction, particular attentionshould be paid to the bamboo strut bearings.Make sure that the hinge parts are firmlybound and cemented in their respectivepositions, and that the brass tube is a smoothbut not loose fit on the wire part. Also notethat the position of the bamboo strip be-tween formers A and B allows the retractingrubber to have a straight pull. This ensuresthat the struts will fit cleanly into theirrecesses.

November, 1939 NEWNES PRACTICAL MECHANICS

Fig. 1.-A vanishing la np showing how the body of the l ',II, collapses into the tray. The sha.le folds up like an umbrella. Fig. 11 (centre) Changing a care&to a handkerchief. The candle is hollow and fits closely into the metal case while the handkerchief is concealed inside it. Fig. l5.-(Right) A colour -

changing candle. A metal shell representing a white candle is drawn down into the candlestick, revealing a red candle in its place

Conjuring with Lamps andCandles

Interesting SecretsMAKING a large lighted lamp sud-

denly disappear is a performancecalculated to surprise any audi-

ence. Fig. 1 shows one of the ways in whichit can be done.

The lamp is permanently fixed to asquare tray. The body of the lamp is con-structed of hinged leaves of metal in muchthe same way as the folding lanterns sold forChristmas decorations. In the lamp illus-trated the body is formed by two separategroups of metal leaves fixed one on top of theother. When not supported these leaves

Fig. 2.-Details of the shade and tray

of Some Puzzling Featshinge and the entire lamp body collapsesflat into the tray.

Fastened to the top of this collapsiblelamp body is a square wire frame the samesize as the tray. The tray and this wireframe are covered with fabric of the samepattern. It will thus be evident that whenthe lamp body is folded down into the traythe fabric -covered square completely hidesit and the tray appears to be empty.

R NormanHunter(The Well-known Conjurer of

" Maskelyne's 114jsteries")

Further Articles on the Secrets ofConjuring will appear Regularlyand Exclusively in this Journal

The Lamp ShadeThis consists of a folding meat cover made

on the same principle as an umbrella. Thefabric is taken off the cover and replacedwith bright coloured silk. A -deep fringe isadded round the lower edge. The measure-ments of the tray are such that when theshade is opened it will fit neatly over thewire frame on top of the lamp body. Theappearance of the complete lamp in thiscondition is shown in, Fig. 2.

The lamp is held erect in its open positionby a thin wooden rod attached to the insideof the lamp shade. This rod goes downinside the lamp body and props it up asshown in Fig. 3. It is only necessary to pickup the shade by the wooden knob on topto cause the rod to be pulled away and themetal body of the lamp to collapse andremain hidden in the tray.

of MagicFinally, light for the lamp is provided in

the simplest manner possible by attaching apocket electric torch to the inside of the shade.The Cloth

To perform the trick, take a large clothof moderately opaque but not too heavymaterial. Throw the cloth over the lamp.The cloth should be translucent enough topermit the light of the torch to showthrough, but not so thin as to permit theactual lamp body to be seen through it.

LOOSE SUPPORTINGRESTING AGAINST

ACROSS PIECE AT TPSHADE 1/ii

2 I

//

Fig. 3.-The wooden rod for holding the lamp inan erect position


SUPPORTINGROD TIED TONSIDE OF

SHADE

Fig. 4.-The thin metal rod attached to the shade

Now, steadying the top of the lamp withone hand and with it grasping the knob ofthe shade through the cloth, place the otherhand under the cloth as though to pick upthe lamp. Gently pull the shade upwardsand as the lamp collapses, ease it down intothe tray quietly. Move away carrying thecloth. The shade keeps it extended as if thelamp were still beneath it. Now with onehand switch off the light and with the otherpress the centre plug through the knob ofthe shade. The shade will collapse and istossed aside in the cloth. I have not givendetails of the shade because these foldingsquare meat covers can be bought for afew pence almost anywhere.

A similar lamp which vanishes suddenlywithout any covering is built, as far as thebody is concerned, in the same way. Theshade consists of a large and small ring ofwire with silk .sewn between. There is nowire square on top of the lamp body, butthe lower ring of the shade is fastened to thetop of the body instead.

The Base of the LampThis lamp is supported by a thin metal

rod passing through the centre of the tray;tnd up to a wire soldered across the top ringof the shade as shown in Fig. 4. Fig. 5shows an enlarged detail of the base of thesupporting rod. A strip of metal workingon a pivot under the tray keeps the rod inposition. To make the lamp vanish the endof the lever is pressed aside by the handholding tray, the rod drops through thetray and the lamp collapses.

In this version the collapsed lamp is hid-den by a spring blind the same colour as thetray. The blind and its roller are built intothe edge of the tray. The roller on whichthe blind is wound is not a spring rollerbut simply runs free. On the opposite sideis a spring blind roller from which theratchet has been removed so that it willrevolve as soon as released. One end of theblind is fastened to each of these rollers.The blind is rather more than twice thelength of the tray and a piece almost thesize of the tray is cut from the end nearestthe spring roller. The result is shown inFig. 6. The spring roller being at tension acatch is arranged so that the descendinglamp will release it. As soon as the blind is

released the portion with the cut out spacewinds rapidly round the spring roller,drawing the solid part of the blind acrossthe tray, concealing the collapsed lamp.

A small pocket lamp globe can be con-nected to a battery under the tray and aswitch arranged so that the light isextinguished as soon as the lamp starts tocollapse. The vanish of the lamp is dis-guised by making a tipping movementbackwards with the tray at the moment thatthe release lever is pressed.

Another sensational lamp trick consistsof shooting a silk handkerchief into thelamp globe. For this purpose a specialpistol is used, the details of which will beexplained in a later article, which vanishesthe handkerchief by winding it up on aspring inside the dummy barrel. Theappearance of the handkerchief, really aduplicate, inside the electric globe is man -

SUPPORTING ARMIN HOLE THROUGHTRAY

10411...-I

PIVOT ))

111 REALgSE

Fig. 5.-An enlarged detail of the base of the..upporting rod

aged as shown in Figs. 7 and 8. Fig. 7shows a small metal container somethinglike a pill box with a hole in the lid. This

-,..BLIND DRAWN ACROSSWHEN RELEASED

CUT OUT OPENING IN BLIND

FREE ROLLER

SPRING ROLLER

FURTHER LENGTH OFBLIND SOLID ON ROLLER

Fig. 6.-The blind and roller built into the edgeof the tray

container is attached to the lamp standardby a length of wire terminating in a ring sothat the ordinary shade ring may be screweddown over it to fix itto the lamp holder.The handkerchief istucked into the metalbox and a generouscorner is left protrud-ing. CONTAINER

At the beginning of.the trick the lamp isalight and a shade isin position over theglobe. The containeris at the back of theglobe. The shade isremoved but owing tothe dazzling effect ofthe naked lamp thespectators are unableto see the containerbehind the globe. Theupper part of thelamp standard workson a pivot actuatedby a spring. When arelease lever is pulledby means of a threadin the hands of anassistant, the upperpart of the lamp makesa half turn, bringing

the handkerchief container to the front(Fig. 8).

The release of the lamp is made to coin-cide with the report of the pistol and thehandkerchief appears to have been shotstraight into the lamp. Again the dazzlingrays of the light prevent the container frombeing seen, but the brightly coloured cornerof the handkerchief is quite visible. Thehandkerchief is now drawn out of thecontainer, coming apparently from insidethe lamp.

This principle of using the dazzling lightfrom a bare lamp to conceal an object canalso be employed for an effective productiontrick. In this case a shaded lamp is broughtforward and the shade removed and shownto be empty. The shade is then replacedand a large number of flags are producedfrom the top of it with the lamp stillalight.

Fig. 9 explains the secret. A fairlylarge black container, open at the top, isfixed behind the lamp. This container ispacked with silk flags and the shade is putover lamp and load container. As long asthe container is kept at the rear it willthrow no shadow on the shade that can beseen by the audience. The shade may safelybe removed, shown empty and replaced aslong as the lamp, which should be a fairlypowerful one and of clear glass, is keptalight. The rays of light dazzle the eyesand completely mask the container. Theshade is then replaced and the flags areproduced from the container, through thetop of the shade.

For the final lamp trick, here is a some-what uncanny feat in which the performerremoves a lighted electric lamp from itssocket and it remains alight in his hands.He then causes the lamp, still alight, tofloat about the stage.

The secret lies in the use of a speciallyprepared lamp. The glass globe portion iscarefully removed from a fairly large elec-tric lamp of the pearl variety. A smallpocket torch battery lamp and case is theninserted into the globe and fixed intoposition with sealing wax or modelling waxor plastic wood. The switch of the torchshould be fixed permanently in the " onposition and the cap at the base of the casemay be loosened when the lamp is to beextinguished.

This self-contained electric lamp is nowput on a standard insiie a shade exactly as

Figs. 7 and 8.-(Left) Detailsof the lamp trickwhich consists ofshooting a silkhandkerchief in-to the lamp

bulb

TOP OF LAMPSTANDARD MAKES

--A HALF TURNBRINGING CONTAINERTO THE FRONT


if it were a genuine lamp and by tighteningthe bap it may be lit when required. Itcan of course be removed and passed fromhand to hand while still alight. Note thatthe lamp holder of the torch should beremoved and _the reflector inverted beforebeing inserted into the electric globe, sothat the torch lamp projects beyond thecase. See Fig. 10B. Fig. 10A shows thecomplete self -lighting globe.

Causing the lamp to float about the stageis simply a matter of a length of blackcotton across the stage with an assistanteither side and a tiny hook on the base ofthe lamp to engage in the thread. Fulldetails of this method of causing objects tofloat in the air apparently without supportwill be found in a previous article of thisseries.

Fig. 11 illustrates a simple piece of appar-atus for turning a candle into a handker-chief. The candle is a metal tube suitablypainted and plugged at one end with apiece of genuine candle. This tube fitssnugly into another metal tube. Thissecond tube is polished and has a lid ateach end. One of these lids is shown on thetable in the illustration. Each lid is amoderately tight fit.

The candle having had a silk handker-chief tucked inside, is put into a candlestickand lit. To perform the change the candle isblown out and slid into the case, the wickend going in last. The lid is placed on andpressed home. When next the case is openedthe other lid is removed, the handkerchieftaken out and the case shown empty. Thehollow candle cannot be distinguished fromthe inside of the case.

The trick can be made up in variousforms. A cheaper method is to use a card-board candle and a cardboard case. This isillustrated in Fig. 12. Note the rim at oneend of the case to prevent the hollow candlefrom falling out when the handkerchief iswithdrawn. Sometimes the metal candleand case is constructed so that the candlefits so closely into the case that it cannot bewithdrawn except by the use of a key thatscrews like a plug into the open end of theshell (Fig. 13).

Instead of changing the candle into ahandkerchief the handkerchief may bevanished and found inside the candle. Thisis accomplished by using a prepared candle.This consists either of a genuine candlewith a hole drilled down the centre toaccommodate the handkerchief, or of a fakecandle made from two pieces of metal orcardboard tube with white paper pastedround, the two tubes joining end to end asshown in Fig. 14. Notice that the joinis not a straight cut, but unequal. The hand-kerchief having been concealed inside, thecandle is in due course broken across thecentre and the silkextracted.

Fig. 15 shows a candle-stick for changing thecolour of a candle. Thecandlestick is hollow and

Fig. 12.-Theshell candle andcase with two

lids

a dummy red candle madeof wood is attached to thebase, passing up insidethe hollow candlestick andprojecting from the top thenormal length of a candle.

There is a white shell, made of thin metaltube, fitting loosely over this red candle.This shell is just the height of the candle-stick and when fully raised completely hidesthe red candle but when allowed to dropinto the candlestiCk, falls right out of sight.A metal stud soldered near the bottom of theshell slides in a slot cut the full length of thecandlestick at the back. The change canthus be made from white to red or viceversa by raising or lowering the shell whilethe candle is hidden by draping a hand-kerchief over it. The shell is maintained inits uppermost position by giving it a slightturn so that the stud rests on top of thecandlestick.

A neat trick of ad unusual nature is pos-sible with this apparatus. A small whitesilk handkerchief is laid over the red candleand the white shell raised to conceal both.In front of the audience the candlestick isshown as containing a white candle. Overthis is draped a small red silk handkerchief.A dark cloth is draped over the candle fora moment and when it is removed thehandkerchief is seen to be white while thecandle is red.

TORCH INSERTEDINTO GLOBE OFPEARL LAMP

TORCH WITHREFLECTORREV RSEQ

Fig. 10.-Details of the self -lighting bulb

The trick is performed by drawing down.the shell; thus biding the white candle andrevealing the red one. The red silk is takenaway with the covering cloth leaving thewhite one visible.

A candle which lights itself and goes outagain on the command of the performer isanother amusing trick. The candle is againa metal tube painted white. Inside is a smalloil container and wick which slides easily

Figs. 13 and 14.- (Left) Thekey for ejectingthe metal candle.(Right) The twoparts of the fake

candle

SHADE CARRIER

Fig. 9.-Pro-ducing a numberof flags fromthe top of alighted lamp

up and down but is prevented, by a flangeat the top of the candle, from coming out.A weak spring under the little lamp keepsit normally at the top of the tube where itsHate is visible. A thread attached to theoil container and passing through the footof the candlestick to an assistant permitsthe lamp, still alight, to he drawn down intothe hollow candle, thus apparentlyextinguishing the candle. A few sihallholes must be drilled at the back of thehollow candle near the top to allow air toreach the flame, otherwise it will go outwhen the lamp is drawn down.

Another effective and very easy trickconsists of lighting a whole row of candlesby passing hand in front of them.Apart from the candles all that is neededis a fake consisting of a tiny metal tubewith a spirit soaked wick. The tube isclipped to the base of the second finger.

The trick is usually perforMed by firstlighting all the candles and then blowingthem out. After that the hand is passedalong the line and the candles light again.The miniature wick in the fake is lit justbefore the candles are first extinguished. Itis then an easy matter to re -light the candlesby passing the open hand in front of them.The fact that they have only just been putout will cause themto light again read-ily. If the candlesare to be lit bymeans of the fakewithout any pre-liminary lightingand extinguishing,the candle wicksshould be touchedwith petrol orparaffin.

Fig. 16. -(Right) sectionof the candle-stick for chang-the colour of the

candle

REDCANDLE

WHITESHELL

HOLLOWCANDLE-STICK

(SECTION)


WORKSHOP WRINKLESBy " MECHANIC "

Useful Hints that Save Time and MoneyA Neat Hydrometer

Drifi StandTHE accompanying sketch illustrates a

rather novel hydrometer stand. A stripof mild steel constitutes the main support,and to this is soldered a brass clip madefrom a strip of ?-in. brass. The mainsupport is recessed into the base, and foursmall rubber feet, screwed on as shown,prevent the stand from slipping. The smalljam jar is also recessed to the depth ofthree thicknesses of ply, and its fitment intothe base in this manner should be tight,yet providing ease of removal whenrequired.

Keej5ing SolderingIrons Tinned

ELECTRIC soldering irons sometimes geta little too hot, and the solder on the

iron becomes covered with a coating ofoxide. This nearly always happens whenthe iron is left for a short while, so toprevent this I kept the copper bit immersedin solder. How this was done is illustratedin Fig. 1, and the tinned part of the bit isthus kept covered with the molten solder,and remains well tinned.

Before I used an electric iron I heatedmy old bit with the point in the solder.This was done by heating the crucible inwhich the bit was resting. The crucible is

ELECTRIC

WALCRUCIBLL E

A novelmethod ofkeepingsolderingirons tinnedwhile in

use CRUCIBLEF'PE CLAY

Fig. I

ALTERNATIVEMETHOD FORGAS IRON

USERS

STOUT

REOVE

WI

Fig. 2

a narrow one, to avoid wasting the heat.The crucible is held in place by a pipe -claytriangle (Fig. 2). A piece of thick wire istwisted round the iron support with theloop for holding the handle of the iron.I heated the crucible with a blow lamp,but any convenient source of heat is suit-able. This method also keeps the ironnicely tinned. The crucibles can be obtainedfrom any chemist.

A Workshoj5 Light-rHIS device consists of a piece of pianoI wire stretched between the walls of the

shed, and this supports a metal fittingwhich carries a lamp in such a way thatthe lamp may be raised or lowered, andby manipulation of a screw it can be

clamped to the wire, or moved along it.The lamp is fed by a length of flex, and theslack in this flex which is produced by themovement of the lamp is taken up by

SOLDERED

An easily madedrip stand for a

hydrometer

BRASSCLIP

HYDROMETER

UNDERSIDEVIEW OF BASE

5 PLY,cle

RECESSEDBASE

TAR

etc., for two years, and the flex is only justbeginning to wear, but will last for anotheryear yet.

The lead weight can be cast by pushinga broom -handle into clay for about 9 in.depth and pouring molten lead in, whilethe lead is still liquid the end of the pulley

T with the hole in it can be pushed in, andwhen the whole is cool, the pulley will befound tq be firmly fixed in the lead. AturnbUckle or wire -strainer is essential, asthe piano wire must be kept very taut.

A Useful Bench Lamy,THE accompanying diagram shows a very

handy and inexpensive bench lamp. Thestem consists of two lengths of j in. by 1 in.+wood, with one side slotted to take the flex,and both tops are slotted to receive the clip.The base is three pieces of wood gluedtogether, with a in. by 1 in. hole in thecentre.

The clip A is folded round the lampholder and fixed by means of a 6 B.A. held

a simple system of pulleys and a weightso that there is a constant tension on theflex which is just sufficient to take up theslack.

The sketch is self-explanatory, but oneor two points may be detailed. The flexmust be of the round braided type ; ifordinary twisted flex is used, the insulationwill wear off at the corners and give riseto trouble. There is, actually, very littlewear on the round flex. I have had alength in use with this system of pulleys,

SOFT METAL OR DRAS5,63_,.FORMING LAMP HOLDER CUP -

Details ofthe woodenframe andwire shadeof the bench

lamp

How toarrange aneat work-shop light

em MOLID.IEDHOLE

LEXT ANCHOREpWOINSULATE)STAPLES

ell,

FLEX0; ROUNDBRAIDEDTYPE

RASS BLOCK

TO BE LARGE ENOUGHR:B MB TO BE JUST FULLEDTHROUGH

by two nuts on either side B. After Securingthe holder, with the flex wired in, run theflex down the slotted stem as shown. Thebase of the stem is tightly fixed into thebase itself, thus holding the wire secure.Any switching arrangement may be usedbut the one shown is very simple.

The shade is made of 18 s.w.g., and theonly point to remember is to leave the fourwires protruding 1 in. Now cut two pieces

SWI)1.' of cardboard and cut a hole in the centre ofeach. One hole should fit the lamp holderexactly, and the other hole should be a i in.larger. Place the card with the larger holeunderneath the four wire ends and the othercard on top, and secure with wire or glue.The cover for the shade can be made from apiece of coloured paper.

-.4 METHOD Of r ; IIII0W RI rarTOF

vs.-

Noember, 1939 NEWNES PRACTICAL MECHANICS 81

"MOTILUS" PEEPS INTO THEMODELWORLD

1 he new lug boat -Mary

WELL, fellow modellers, now isthe time when indoor modellingshould be at its height. Let us

hope this year it will be the same as ever,for it is up to us all to carry on. This monthI bring you news from a model railwayenthusiast in British Guiana, Mr. A. Smith,of Berbice, who sends this picture of hisscenic railway layout. " It is an enormousattraction at our house," says Mr. Smith," and is besieged with visitors of all ages.Also it has made money as a side show atbazaars, etc., with the operator of thedistant contr 31s hidden behind a screen."As you have already guessed no doubt, therailway is a Twin Train Table Railway,with the scenery carefully painted to repre-sent the natural colourings. This cannot beseen to best advantage in a photograph,but Mr. Smith has developed a techniqueof papier maths, coated with sand and saw-dust which gives a realistic representationof bushes and grass in this scale. The roadsare painted to represent tar macadam, therocks are real stones, and all the buildingsare lit up. To prevent the whole being toosombre the arch facings and buildings arepainted in unnaturally bright shadesbecause " after all " (in the words of theowner) " the layout is a toy and not a modeland this gives the happy finish." Person-ally I feel it has many ' model " points !A New Tug Boat

I wonder how many of you have seen thenew tug boat placed on the market byLiras l'rnq P is construetrtd rf on- of the

new plastics and the detail, even in thesmall life boat on deck is amazing, and justgoes to demonstrate the possibilities of thistype of manufacture when large quantitiesof a model can be placed in work. It is7 inches long by 2 inches wide and housesan efficient little clockwork mechanism.The hull is black with white deck andbrown deck houses. The funnel is red andblack. Fittings include the aforesaid

The mo:Tel

railwaylayout ofMr. Smith,of British

Guiana

"I he G.W.R. "Peridcants Castle.'

It is up to the Amateur ModelMaker and Owner to Keep InterestAlive in this Vial Hobby-for it isone wh'ch mai be Badly Hit by

Poor Trade.Our Model Fan with his CameraFinds News of Wartime Model

Making.

dinghy on deck, ventilators, bollards,capstan, bridge with steering wheel and twostarboard engine room telegraphs, two life -I ,uoys, port and starboard lights, etc. --quite a collection ! The cost of the modelat the moment of writing is 7s. 6d., but withthe outbreak of hostilities there is almostcertain to be an advance on this. It can beobtained from Messrs. Hamleys, Bassett-Lowke's, Lucas of Liverpool, and at manyof the leading toy shops in London and theprovinces, and also a set of finished partsis available at 3s. 9d. the set." Cock of the North "

I was in London last week and noticedthat Messrs. Bassett-Lowke have in their

shop a very fine unpainted model of theL.N.E.R. type of locomotive " Cock of theNorth," inch scale, 2 inch gauge. Thoseinterested in high-class hand -made steammodels should call in and see this_piece ofwork by expert craftsmen, as they may beable to get some ideas from it.

Of recent times Bassett-Lowke havebegun to cater more and more for the ownerrequiring a special Gauge " 0 " hand -mademodel in clockwork or electric, made upat a reasonable price using standard parts:Mr. Gilbert Thomas, the well-known writerand critic, who has now removed fromLondon to Teignmouth, has just added tohis line a G.W.R. 4-6-0 " Pendennis Castle."He told me that he is now well on with the


re -erecting of his gauge " 0 " railway, andthat the price for the detail work of thisspecial hand -made " Pendennis Castle "was 13 guineas all told, which appears to bevery reasonable. He seemed to think so forhe is ordering another G.W.R. locomotive,the " Llanfair Grange," No. 6,285, from thesame firm. I am showing a picture of the" Pendennis Castle " model. Its prototypeyou will remember holds the remarkablerecord of making better times on a lowercoal consumption than one of the 92 ton" Al " class Pacifies on the L.N.E.R., inthe " exchange " trials of 1925. Incidentallythe Castles are 80 ton expresses and theyhave been more extensively built than anyother G.W.R. passenger type. They areresponsible for many important dutiessuch as the 71.4 miles -an -hour " Chelten-ham Flyer " and the 67.6 miles -an -hour" Bristolian," the fastest trains on the line.Model Aeroplane

Model aircraft is in the picture again,and in gorthampton I was lucky to see abatch of civil aeroplanes and flying boatsthey were making for the Nen, Zealandexhibition, to show the progress of Britishcommercial aircraft in recent years. Theeight 'planes were made of African whitemahogany wood, silver lacquered to givea metal finish and were made over a perio Iof five weeks. The engines and nacelleswere of metal and the machines modelledwere the D.H. 91 " Albatross " G-AFDI,the D.H.95 " Flamingo " G-AFUE, Arm-strong Whitworth " Ensign " G-ADSR(shown in this picture), Short " G " classflying boat, short " S.30 " class FlyingBoat (4-AFCI, Fairey " F.C.I.," HandleyPage " Hannibal " and the famous Mayocomposite 'plane." Gradients "

Each month I like to give you news of

The new gauge "00" gradients for the T.T.R.railway

some new gauge " 00 " development, andthis time it is ".gradients." Some of you, Idare say, have visited Bassett-Lowke's atHigh Holborn and seen their working dis-play of the Twin Trains in the basement.This layout now includes gradients forhigh level tracks, and this novelty in gauge" 00 " is proving so popular that they haveworked out a standard set which providesfor a gradient of 1 in 30 in a length of8 ft. 6 ins. At the top this gradient gives a3 inch clearance. Fellow modellers willrealise the big possibilities of this gradientset-the number of high and low levelroads they can arrange by using thesestandard fitments, which consist of straightand curved sections, special sections for

At work on the Armstrong Whitworth Ensign G-ADSR model

points and piers of varying heights. I hadthe opportunity of examining a set of thesegradient parts. The sections and supportsare All made of African white mahoganyfree from knots and shakes and finishedin a matt colour to represent modernconcrete construction. If you want brickpiers, it is a simple matter to cover thesewith brick paper, which can be obtained inall types and colours as low as 3d. a sheet.My picture shows a typical under and overroad, with a T.T.R. goo Is train above andthe new L.M.S. " Coronation Scot " passingon the under road. The standard " Lowko "set as it is called consists of : 2 tapered trackbases, 6 piers of varying heights and 5

straight track bases 141 in. long x 21 in.wide. The two tapered track bases carrythe track from zero to 1 inch and the pierslettered A to F continue the graduationfrom that height to 3/ in. to the top of thetrack base, making a total length of 8 ft. 6in.Complete set costs 15s. 6d., and parts areobtainable separately.

Famous Motor YachtIn these times of stress, it is pleasant to

remember the yacht racing synonymouswith the name T. 0. M. Sopwith. I haverecently come across this picture of anexcellent model of his famous motor yachtPhilante, modelled for the makers, Messrs.Camper and Nicholson of Southampton.Designed by C. E. Nicholson, M.Inst. N.A.,the Philante was launched at Southamptonon February 11, 1937, and underwentsuccessful trials at the end of May of thatyear. Her principal dimensions are overalllength 263 feet, extreme breadth 38 feet,tonnage (Thames measurement) 1,612 andcruising speed 14 knots. In my opinionthis vessel is the ideal. of what a steampleasure yacht should be. At the time of hertrails she was the largest yacht built in theUnited Kingdom, while her M.A.N. Dieselmachinery, which develops 3,000 totalB.H.P. on normal fuel setting, gives her avery useful turn of speed. The modelshown here is to a 'scale of 1 inch to one foot.

A in. to the ft. model of the motor yacht, -Phi/ante-


PRACTICAL MECHANICS " WIRELESS SUPPLEMENT -

P.M. Short-wave ThreeA short-wave Receiverof the " Straight" typeDesigned to Satisfy theneeds of those Enthusiastswho Require an Efficientyet Simple Installation

Mhave been the requests for

a superhet receiver designed forbattery operation, and for short-

wave reception.Quite a goodly number still favour a good

straight receiver something along the linesof what is often affectionately called bythe old timers - old faithful," or, inother words, a circuit of the single H.F.type followed by an efficient detector, andone or two stages of L.F. amplificationaccording to individual requirements.

A circuit of this type has much to recom-mend it for every short-wave enthusiast'sconsideration; it is invariably reasonableas regards price, simple to construct and,once its operating characteristics havebeen rendered more or less perfect, quitepleasant to operate, and reasonably con-sistent in performance.

We are not overlooking the fact thatin these days of station -swamped ether,one has to face the ever-increasingproblem of selectivity and we fully realisethat the super -het, plus or minus a crystalgate, goes a very long way towardseliminating the hug -bear of interference.While giving all due respect to theseitems, it cannot be denied that such outfits

are not within the range of every reader'spocket, and it would not be any exagger-ation to say that the mass of short-wavelisteners have to be content with somethingrather more modest than a receiverembodying all the refinements suggestedabove. It is, therefore, in an endeavour toprovide a good all-round receiver that thisset has been designed.

The CircuitThe theoretical diagram shown in Fig. 2

depicts a three -valve circuit.The initial aerial circuit consists of an

Eddystone three-iwinding coil, one of whichis used for aerial coupling, another for thegrid input circuit, and the other one for thereaction. It will be noted that no badspreading, in the ordinary sense, is pro-vided. This was found to be unnecessaryas the special type of mechanical driveused in the slow-motion tuning gear,provides an identical effect with theadvantage of definite dial recordings.

The grid coil, which is tuned by anEddystone .00016-mfd. variable condenser,type number 1131, feeds the detector viathe usual leaky grid coupling col denser.As sensitivity and gain are iml3rtantfactors, it was decided to use an S.G. valve

"sow

7

5%

14

Fig. 1.-Drilling diagram for the panel

3%B.

4,3'8 DA

34DA

Ow

A three-quarter front view of the receiver

in this position, as it not only gives agreater output on a weak signal but it alsoallows a very efficient form of reaction tohe obtained.

The output from the detector is fed intothe first L.F. stage by means of a resistance -capacity coupling, and it will be noted thata volume control has been fitted across thegrid circuit of the first L.F. to enable theultimate output volume to be regulated sothat headphones or speaker can be used asdesired.

The coupling between the first L.F.valve and the output stage is provided byan L.F. transformer of the yarley Niclettype, but, to prevent the primary receivingan excessive current load, it is arranged inthe normal parallel -feed method which,incidentally, also provides a certain degreeof decoupling.

The output valve is a Cossor 220 H.P.T.pentode which is quite capable of providing

LIST OF COMPONENTSOne Eddystone type No. 1131, 160 m.mfd.

var. condenser.One Eddystone type No. 969 six -pin coilholder.Two Eddystone type No. 949 four -pin valve -

holders.One Eddystone type No. 950 five -pin valve -

holder.Two J.B. .0001 mfd. var. condenser, type No.

2146.One Bulgin H.F. choke, type No. H.F.3.Fixed Condensers-Dubilier : Type 4601/S :

One .0001 mfd. ; one .01 mfd. Type4602/S : One .05 mfd. Type 4603/S : One0.1 mfd. Type 4608/S.: One 0.5 mfd.Type 4609/S : One 1 mfd. Type 3016 :Two 2 mfd.

One chassis (Peto-Scott), 14 x 9 x 3.One panel (Pero -Scott), 14 x 9.Fixed resistances-Erie. I Watt : Ore I meg.,

one 0.25 meg.. one 10,000 ohm ; one 0.1meg., one 50,000 ohm, one 20,000 ohm,one 100,000 ohm, one 15,000 ohm, one30,000 ohm.

Potentiometers-Erie : One 0.25 meg., one50,000 ohm, with switch.

L.F. transformer. One Varley Niclet D.P.21.L.S. panel (Clix).A1, A2, and E socket strip (Clix).Valves, Cossor 210 S.P.T., 210 H.L., and 220

H.P.T.Coils-Eddystone : 22.47 metre, No. 959.6Y.


I

0

.5,0000

5MFD.

L4/FHONCS

/

M.

0, TO.

B. +

G.B. C.S.

Fig. 2.-Theoretical circuit diagram for the short-wave three

adequate output for all normal purposesand, providing the volume control is usedin the manner intended, it will handle allthe input necessary for full output.

It will be seen from the above descriptionthat there is nothing fanciful about thecircuit, and that no unnecessary com-ponents or gadgets have been embodied ;therefore, it should present no difficulties toany enthusiast as regards its construction;in fact, it is quite a safe proposition fora keen beginner to consider.

LayoutThe plan drawing of the chassis, Fig. 3,

shows that a very clean and clear layouthas been obtained, and it should also benoticed that no attempt has been made tosacrifice space to make the overall dimen-sions smaller.

The main tuning condenser, togetherwith its mechanical band -spreading drive, islocated in as dead central position, whichnot only gives a pleasing appearance to thepanel but also allows the controls to beplaced at the most convenient operatingpoints.

As a steel chassis was used in the originalmodel, it was decided to use the speciallow -loss baseboard -type valve holders pro-duced by Eddystone, and, as each valve-pin,socket on these holders is made in onepiece, the possibility of contact noise] isconsiderably reduced.

By employing a chassis, the majority ofthe components are housed out of sightand well protected, while the wiring isconsiderably simplified as is evident by theplan drawing of the underside of the chassis.

To avoid the use of plugs and jacks thespecial Clix switching output panel isemployed and, for convenience' sake, it hasbeen fitted on the right-hand side of thechassis when it is viewed from the front.This simple device allows a most rapidchange -over to be made from headphonesto loudspeaker, and, when housing thecompleted set in a cabinet, no difficultyshould be experienced in making a suitableaperture for access to this component.Assembly

Before proceeding with any drilling, layout the components to be mounted on thetop of the chassis on the actual metalchassis and carefully mark off the exactpositions for the holes to be drilled, aftermaking quite sure that all the componentsare in the positions indicated by the plandrawing. After drilling, clear all holes ofburrs, and then repeat the procedure forthose parts which have to be mountedinside the chassis. Don't attempt to fixanything down until all drilling is finished,otherwise damage might be caused to

certain components which will not onlyspoil the appearance of the completedassembly, but also possibly affect theefficiency. Particular care must be takenwhen setting up the bracket which supports

0

0

9O MFD

GB -2

Ls

0001MFD

to

16 ;5 17

the main tuning condenser, and the locatingand fixing of the slow-motion drive. Don'ttry to rush this part of the work. Rememberthat the drive is dead central along ahorizontal line of the panel, and that thedistances of its fixing, and that of thecondenser bracket from the front panel, arevery important.

For satisfactory fixing of all parts boltsshould be used, and, for a thorough job,use shakeproof washers under each nut.The Panel

This can be purchased, the same as thechassis, from Messrs. Peto Scott readydrilled but, if you wish to do it yourself,check all drilling points before startingthat operation. The large hole for the dialshould be scribed on the metal, and thencut out with a fretsaw, the edges beingsmoothed off with a small file.

When handling this part of the assembly,see that the bench is free from all metalfilings, and covered with two or three layersof stout paper, otherwise the fine polishedfinish of the panel will soon be marred. Itis attention to these little details whichmakes all the difference in the appearanceof the set when completed.

Fig. 3.-Wiring diagramof the receiver

4,/\ 07

;Mn

TOVACLAVPECF

00016 MFD

+30,00011 MC

00.000

G.B.-1.25MCI

2MFD

2 MFD.

is,000n.

50300

20,000 C-)

50,000

111111',4P10,

A2 Al

As A,

0.6.-P

Ig

M.0


PHOTO -ELECTRIC EXPERIMENTSPOLISHED METAL PLATEAPPROX 3' SQUARE

-EBONITE

"E-SCREWHEADS

Fig. 1.-A simple apparatusfor demonstrating the photo-

electric effect

IT is known by all television amateurs thatthe modern photo -electric cell owes itsorigin to the discovery made in 1888

by Hallwachs, a German physicist, thatareas of certain metals, when stronglyilluminated by violet, or, better still, byultra -violet rays, lose almost immediatelya charge of negative electricity" which hasbeen previously imparted to them. Thiseffect is usually known as the' "Hallwachseffect."

In addition to the above, however, it wasdiscovered also that an uncharged insulatedmetal plate is able to acquire a positivecharge when ultra -violet rays fall upon it.Such phenomena were studied by a numberof scientists, and, eventually, they gave riseto a device of supreme practical importance-the photo -electric cell.

It is possible for the amateur to make anumber of interesting experiments basedupon the early observations of Hallwachsand others. Such experiments are easy tocarry out and they are of value in view ofthe fact that they illustrate in a verydefinite and striking manner the funda-mental principles of the photo -electric cell.

In the first of these experiments con-struct the apparatus shown in Fig. 1. Itconsists of two small wooden bases, approxi-mately 4 by 2i in. in area. Each base hasan ebonite upright. To one of these up-rights is secured a piece of coarse wiregauze. To the other upright is fixed ametal plate, the plate being fastened bymeans of a lump of plasticine or a dab ofsealing -wax placed at the back. The metalplate should be about 3 or 3i in. square,the area of wire gauze being about the samedimensions also.

Preparing the PlatesA number of plates of different metals

should be provided, such as plates ofcopper, zinc, sheet iron, tinned iron,aluminium and brass. It is absolutelyessential that these plates should be broughtto a high polish on one side. A mirror-likesurface is not essential, but the platesshould be rubbed over first with coarse andthen with fine sandpaper (with- the excep-tion of the tinned iron) in order to exposea fresh and untarnished surface to the lightaction.

Connect a wire to the gauze and connectup the other end of the wire to one terminal

COPPER PLATES

LIGHT-SENSITIVE CELL(COPPER PLATES INCOPPER SULPHATESOLUTIONCONTAINED INJAM JAR)

'''RUBBERBANDS

EBONITE SHEET

A Number of Simple and EasilyPerformed Photoelectric Ex-periments which Demonstrate theUnderlying Principles of the

Photoelectric Cell.

OUTPUT TO -AMPLIFIER'PHONES ORMiLuAMMETER

the plate, otherwise the H.T. battery cir-cuit would be completed and the galyano-meter probably ruined.

Note now the galvanometer reading. Itwill be seen that no current flows. Nowtake a few inches of magnesium ribbon andburn it in front of the metal gauze and at adistance of about 6 in. away from it. Theburning magnesium will flood the metalplate with ultra -violet rays. Instantlythe galvanometer needle will be deflectedshowing that a current is passing. Moreover'

CLOSED CARDBOARD BOX

Figs. 2 and 3.-(Left) Details of the light-sensitivecopper cell construction, and (Right) Showing an

experiment with liquid light-sensitive cells

of a galvanometer or other current -indicat-ing instrument, the more sensitive thebetter.

Next connect another wire to the metalplate and the other end of this wire to thenegative terminal of a radio high-tensionbattery which should possess an E.M.F. ofthe order of 100 or 120 volts. The positiveterminal of the H.T. battery is connectedto the galvanometer, thus completing acircuit from metal plate to metal gauze.

Before making these connections be surethat all the apparatus (H.T. battery andgalvanometer excepted) is perfectly dry.If you have any doubts upon the matter itis best to place the wooden stands supportingthe metal plate and gauze for half anhour in a warm oven in order to drive offtraces of moisture which would very prob-ably ruin the experiments.

Having fixed up the apparatus as shownat Fig. 1 and described above, move thewire gauze assembly up to the metal plateso that the gauze faces squarely up to theplate and is separated from it by a space ofabout or 4 in. (not more). On no account,however, must the gauze actually touch

APERTURE OR"WINDOW"

JcHT SOURCE

as the burning magnesium ribbon is movedup to the wire gauze the galvanometerdeflection will increase, whilst if themagnesium ribbon is withdrawn from thegauze the galvanometer needle will show adecreased deflection, thus proving that thecurrent -generating property of the ultra-violet light is proportional to its intensity atthe metal surface-a law which governsrigorously the functioning of all light-sensitive devices.

The Effect on the PlatesRepeat the above experiment with the

various metal plates. It will be found thata zinc plate gives the best results. Afterzinc comes aluminium. Copper, brass andtinned iron show a very considerablydecreased effect and sometimes, if they arenot highly polished, they do not show it atall.

What is the expination of the aboveeffect ? It is not difficult to grasp. The metalplate, being connected up to the negativepole of the H.T. battery, is negativelycharged. When the plate is acted uponbl ultra -violet rays it loses a portion of its


charge. Thus the equilibrium of thebattery circuit is disturbed and a smallcurrent flows.

It will probably be found that any givenmetal plate will only show the photo-electric effect in this manner a certainnumber of times-say, half a dozen times.After this it will undergo a species of"photo -electric fatigue." This is due tothe slight tarnishing or surface oxidationundergone by the plate. If the plate isrubbed over thoroughly with fine sand-paper so as to expose a fresh surface, it willbe found to show the photo -electric effectas well as ever.

The underlying cause of the photo-electric effect is readily grasped. When alight ray of a certain vibration-frequency-a ray of ultra -violet light, in the abovecase-falls upon a polished metal surface,it knocks away from one of the surfaceatoms one or more electrons, the electronsbeing shot off from the metal surface in amanner similar to that in which they areemitted from a heated valve filament,although less copiously. The H.T. batterysimply supplies a "driving potential," theelectrons being caught by the gauze screen,the circuit thus being completed.

The photo -electric effect is best shown bythe alkali metals, potassium, sodium,rubidium and caesium. Such metals,although they enter into photo -electric cellconstruction, cannot be employed in theabove experiments because, in contact withair, the surfaces instantly become coveredwith a layer of oxide. In photo -electric cellssuch metals remain bright indefinitely onaccount of the absence of air in the vaccumcells.

Besides metal plates certain crystals arelight-sensitive and can be made use of inthe above experiments. If, for instance,instead of a polished zinc or aluminiumplate we employ a crystal of galena, thewell-known wireless rectifying crystal offormer days or, better still, a piece of molyb-denite, the same effect will usually beobtained with the apparatus described.Not all galena crystals are sensitive inthis manner. Their 'sensitivity dependsupon some unknown factor. Hence, theexperimenter who has a quantity of galenacrystals available will have to play thegame of trial and error with them until hehits upon a crystal which displays stronglythe photo -electric effect.

Other crystals which are similarly photo-electric are chalcopyrite and iron pyrites,both of which were formerly well-knownas radio rectifiers.

Liquid Light -Sensitive CellsThese cells provide a large field for

amateur experimentation. One of thesimplest cells of this type is seen at Fig. 3.It comprises two copper sheets, approxi-mately 2 x 1 in., which are cut with anattached lug, to which a connection maybe made. The copper sheets should be wellcleaned by rubbing them over with strongsoda solution, then by rubbing them withcoarse and, finally with fine sandpaper. Asuitably -sized piece of ebonite sheetseparates the copper plates which areattached to it by means of two rubberbands.

Make up a 1 per cent. solution of coppersulphate (about 5 grains of copper sulphatein an ounce of water is the right proportion)and stand the copper pates in a vessel con-taining this solution. Preferably, a threeor four days' immersion should be allowedand the immersion should be carried outin the dark.

After a few days the cell will have" formed." A fine coating of copper oxide

will be present on the surface of the plates,this thin film being light-sensitive.

Now obtain a cardboard box sufficient-ly large to contain the cell. Make anaperture in the side of the box so that lightpassing through this " window " may fallupon one of the copperplates of the cell, theother being unillumined. Connect leadsfrom the copper plates to a pair ofheadphones or to the input terminals ofa radio amplifier equipped with a loud-speaker.

On holding a bright light -source near tothe " window " of the box and interruptingthe light more or less rapidly by jerking asheet of cardboard up and down in the pathof the light rays, a series of clicks will beheard in the 'phones or loudspeaker, these

clicks being generated by pulses of currentfrom the light-sensitive cell.

A cardboard disc provided with radialslots will, when revolved in the path of thelight rays, give rise to a humming noise inthe phones of speaker. Also, if by anychance a miniature arc -light can be obtained,it will be possible to listen -in to the irregularpulsations of current passing through thearc.

Needless to say, all these effects may bestudied by substituting a sensitive micro-meter in the external circuit of the cell inplace of the phones or radio amplifier.Micro -ammeters, that is to say, instrumentswhich read down to a few millionths of anampere, are costly articles, however, andnot many experimenters possess them.

AROUND THE TRADEModel Maker's Box Spanner

BONDS 0' EUSTONROAD, LTD., have just

marketed a model maker'sbox spanner which has beenspecially made to fit the M.E.

A model maker'sbox spanner

size Whitworth nuts and hexagon bolts,which as readers know are smaller acrossthe flats than the standard Whitworth sizes.

Spanners can be supplied for A -in.,A -in., *-in. and A -in. M.E. sizes of nuts.The price per box spanner is 9d., pluspostage.

A.R.P. HandlampCASCO ELECTRICAL S)RVICE have

recently marketed a portable hand -lamp which has a number of uses. It isconstructed of 18 S.W.G. metal, has aswivel handle and a hinged lid fastener.

The inside of the box is painted withanti -sulphuric paint, whilst the outside ofthe case is black crinkle. The photographshows the neat and novel appearance of thelamp. The light is fixed on top of the lid

A portable hand lamp suitable for A.R.P. worker

and the 6 -volt bulb is a double pole, dualfilament which gives an even diffused light.It is worked from a 6 -volt " Dagenite "unspillable accumulator and the terminalsof the battery are insulated and cannotshort circuit. The lamp will give a con-tinuous bright light of 12 -watt candle-power for 9 hours or a continuous dimlight of 3 watt candle -power for 20 hours.Using an intermittent light it will give250 hours' service. The lamp costs £3 19s. 6d.

The " Compact " Patent LadderTHE Southern Ladder & Step Co.,

have recently produced an ingenioustype of ladder which actually shuts up.It differs from the ordinary folding or

The"Compact-patent ladder

collapsible types and has been designed foreasy carrying and convenient storage. Aswill be seen from the sketch, it takes up theminimum of space when closed and whenopen is held rigid by means of a metal barand a wing nut. The uprights are madefrom selected well seasoned timber and therungs are made from oak. When closedthe rungs fit into special grooves cut intoeach side of the uprights. The ladder is8 ft. high (open) and costs 25s. A 10 ft.ladder can be obtained for 5s. extra.


" That's an odd way to work,"remarked Blewitt,

Are you sure, dear old boy,you won't rue it ?"

Said Brown," That's all right,See! I'm using FLUXITE.So you see, on my head I can

do it ! "

See that FLUXITE is always by you- in the house garage-workshop -

wherever speedy soldering is needed.Used for 30 years in Governmentworks and by leading engineers andmanufacturers. Of Ironmongers -intins, 4d.,8d.,1 4 and 2 8. Ask tolsee theFLUXITE SMALL -SPACE SOLDER-

ING SET --complete but substantial complete with full instructions 7 6. Writefor Free Book on the ART OF " SOFT " SOLDERING and ask for Leaflet onCASE -HARDENING STEEL and TEMPERING TOOLS with FLUXITE

TO CYCLISTS ! Your wheels will NOT keep round and true unless the spokesare tied with fine wire at the crossings and SOLDERED. This makes a much

stronger wheel. It's simple --with FLIJXITE - but IMPORTANT.

THE FLUXITE GUNis always ready to put Fluxiteon the soldering job instantly.A little pressure places theright quantity on the rightspot and one charging lasts forages. Price 1/6, or filled 2,6.

ALL MECHANICS WILLHAVE

FLUXITEIT SIMPLIFIES ALL SOLDERING

FLUXITE Ltd., Dept. P.M., Dragon Works, Bermondsey St., S.E.I

CURE FOR 'BLACK -OUT' BOREDOMBuild a Model Aeroplane, which can easilybe constructed without any special tools

MegowBalsa Flying KitsKits for 24in. wing span FlyingModels of the STINSON RELIANT,WACO CUSTOM, MONOCOUPE,CONSOLIDATED P/30,FAIRCHILD,HAWKER FIGHTER, CURTISSHAWK, RICHMAN AND

MERRILL'S VULTEE.PRICE 216. Postage 4d.

Large range of smaller kits to make up 12" Flying Models.PRICE lld. Postage 3d.

Or start a Model Railway, and commence by layingthe track with Bond's "00" or "0" GaugeTrack Parts

PRICES. Gauge "00" Parts Steel Chairs ... ... per 100 I 4Steel Rail, sheradised finish Fishplates ... per doz. 3d.

per yd. I fd., 1/3 doz. yds. Sleepers, Wooden ... per 100 Bd.Brass Rail per yd. 3d., 2/3 doz. yds. Electric Raised Chairs ... per doz. Bd.Cast Chairs ... per 100 1/4 Pins 3d. packet

PRICES. Standard Gauge "0" PartsSteel Rail, sheradised, per yd. 2d. I'S doz. ydsBrass Rail ... ... per yd. 40. 4'3 doz. yds.Cast Chairs, slide -on fit ... ... per 100 1/2Electric Raised Chairs ... ... per 100 2' -Fishplates ... .. per doz. 3d.Sleepers, stained correct colour ... per 100 2.3Battens, Fn. x i-in. section

per yd., 21d., 2/3 doz. yds.Pins, approx. 1,000 ... 6d. packet

Track Gauge, special, with elec. chair -jig9d. each

All Track prices plus 10%. Plus Postage.

SEND FOR BOND'S 1940 GENERAL CATALOGUE, PRICE 6d.; THIS WILLINTEREST YOU AS ITS 208 PAGES ARE FULL OF PARTS REQUIRED BY

THE MODEL MAKER INCLUDING TOOLS AND MATERIALS.

BOND'S 0' EUSTON ROAD LTD.357, EUSTON ROAD, N.W.I

'Phone EUSton 5441-2 Established 1887

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FIXING OFDETACHABLE SHUTTERS

RAWL 4j-1-

IRAIAII

The War Office, Air Force, Admiralty, G.P.O., Metropolitan Police,L.C.C., and Municipal Authorities everywhere, have universally adoptedRawlplug Fixing Devices-they are using them for securing A.R.P. shutters,swing shutters, black -out curtains, partitions, electric light fittings, clothesracks, brackets for fire equipment, seats, ventilation,and air filtration appliances, etc.

DARKENING OF WINDOWS :The Government has stated that plans are beingmade on the assumption that war may last for3 years, owners of premises are, therefore, takingimmediate steps to replace their temporaryA.R.P. fittings with more permanent ones, whichcan be conveniently operated.There is a Rawlplug of a size and type for everyclass of work, from the fixing of curtains andblinds to the holding down of heavy machineryand other fixtures where a strain of over zotons may have to be contended with.

Blast, Splinters and Flying Glass: The best way to obtainprotection against blast, splinters and shattered glass is to fit metal or woodenshutters over the windows: At nights, shutters serve the dual purpose ofprotecting against blast and obscuring the light, thus obviating the need forblinds or curtains. Rawlbolts or Rawlplugs ensure that these shutters arefixed quickly and absolutely securely without damage to walls or decorations.

Write for copy of ourlatest "Fixing Devices"

book and special A.R.P.

folder.

B.240

The Raw;p!ug Co., Ltd., Rawlo!ug House, Cromwell had, London, S.W.1

WAR -TIME RESTRICTION OF PAPER SUPPLIES

ORDER FORMFOR READER'S USE TO NEWSAGENT OR BOOKSTALL

To(Name of Newsagent or Bookstall)

Please deliver or reserve for me copies of each issue of PRACTICAL MECHANICS until further notice.

Signed

Address

N.B.-This Order Form, if sent to the reader's usual Newsagent or Bookstall, will ensure regulardelivery of this magazine during war" time. Paper supplies have been rationed to all publishersand the wastage of unsold copies in the shops must be avoided. Please help both publisherand retailer by ordering NOW.


urInk Detective

THEinquisitive person-vulgarly

known as " Nosey Parker "-will havehis or her curiosity baulked by a newsteam -sensitive ink. When printed on theflap' of an envelope, this ink, under theinfluence of steam, changes colour. Con-sequently, a printer's inkling is given thatthe envelope has been tampered with bysome Paul Pry or his feminine equivalent.

Nonslip Bowl for PetsI N taking its food from a vessel placed on

the floor, an animal is apt to push itabout and spill the contents. A new non -spill combination food and drink bowl fordogs and cats has been contrived. Thisvessel will not slip nor tip on the smoothestwaxed linoleum. A patented rubber baseprevents it from skidding. The bowl hastwo compartments, each holding a quart.And this receptacle being made of Bakelite,there is no fear that Bonzo will have chipswith his fish.

Antidrip GadgetWHEN the umbrella has been on duty

in a pelting shower, it has a bad habit oftreating the floor of a room as an umbrellastand. Therefore, an anti -drip catchingattachment, which has been patented in theUnited States, will be acceptable. It con-sists of a hollow, resilient, cylindricalarrangement affixable to the umbrella in theneighbourhood of the ferrule.

Paper BibsTHEHE bib has for many a long day shielded

dress of the babe from waywarddiet. A patent for a newly -devised paperbib has been granted by the United StatesPatent Office. The bib has extensionsarranged to encircle the neck of the juvenile,and glued on it are straight narrow strips ofreinforcing paper. The youngster would beintrigued vire this dress protector decoratedwith pie es of Jack Horner, LittleRed Riding Hood and other charactersdear to the natives of the nursery.

Medicine MusketTHE giving of medicine to children and

animals requires a blend of coaxing andcoercion. As regards the horse, the veter-inary surgeon used to employ a bottle or ahorn, which he inserted in the side of thehorse's mouth. The contents of this con-tainer were sometimes evenly distributedbetween the internal economy of the sickquadruped and the sleeve of the operator.

But the modern horse doctor can availhimself of a veterinary dose gun, which hasbeen patented in the United States. Thiscomprises a tubular nozzle and a piston, andthe medicine is fired, so to speak, into thethroat of the four -legged patient. In usingthis medicine musket, the " vet " adminis-ters what may be termed a gun -powder.

Puncture AlarmWHEN a tyre on a motor trailer goes

flat, it is not at once apparent to thedriver of the preceding vehicle. To summonattention to this defect, there has beendevised a metal clacker which gives a

usy InventorsBy " Dynamo "

definite warning to the driver that one ofthe tyres on the trailer has declined from itsnormal rotundity. The clacker is mountedon the rim, touching the tyre. As the tyreis deflated, it presses against the clackerand, with each revolution of the wheel, nouncertain sound informs the driver thatsomething untoward has happened.

Brow MopTHE primal curse upon the ground,

making it necessary for man to earn hisbread by the sweat of his brow, was ablessing in disguise. And the beads ofhonest sweat which bedew the forehead of thevillage blacksmith are intrinsically of greatervalue than the jewels that gem the -crown ofa monarch. But this sweat, which ourrefined Victorian forbears termed per-spiration, is at times inconvenient. Forinstance, tennis players and other folksengaged in vigorous sport, not to mentionthe horny -handed sons of toil, find the tinyrivulets which meander across the featuresare apt to blur the vision. To dam thesestreams, a sweat pad has been devised andpatented in the United States. Thisabsorptive mop for the brow will preventperspiration from cascading down thecountenance.

The following information is specially supplied to"Practical Mechanics" by Messrs. Hughes & Young(Eat. 1829), Patent Agents, of 9 Warwick Court, HighHolborn, London, W.C.1, who will be pleased to sendreaders mentioning this paper, free of charge, a copyof their handbook, "How to Patent an Invention."

Di used AirwaidWarningsI T is contended that the effective range of

air-raid warnings, even when powerful,are limited. Less strident and more numer-ous alarms are said to be preferable. Actingupon this belief, an application has beenmade to the British Patent Office to protectan idea embodying the principle in question.It is pointed out that, when air raids areexpected, normal lighting is extinguished.The lighting fittings are then available foraudible alarms, and devices for thesealarms may be adapted to be readily sub-stituted for lamps. The alarm device is pro-vided with a cap to co-operate with the lampsocket in a street -lighting fitting. And it isso constructed that it can be worked by thesupply of electricity to which the socket isconnected. One cannot predict that thearrangement will be generally adopted, butan important company has sponsored thisalarming invention.

For the Modern CiceroPPUBLIC speakers are of two sorts. There

is the born orator, whose eyes are notglued to a manuscript. He prepares histhoughts but relies upon the inspiration ofthe moment for the language with which heclothes them. Like an artesian well whichbubbles up scintillating in the sun, hisfountain of sparkling words rises to thedelectation of the enraptured audience.But he is the exception. The averagespeaker, if he does not actually read his

speech, depends upon notes, to which hemakes frequent reference.

To help the latter type of spokesman, aninvention has recently been submitted tothe British Patent Office. It happens to bethe conception of a subject of the GermanReich, and is an apparatus for facilitatingreference to a manuscript by a speaker.Lecturers generally use manuscripts whichare either horizontal or upwardly inclinedon their desks. From time to time, thelecturer glances at his manuscript. In sodoing, his gaze is diverted from his audience.This means some loss of power over hishearers, as the eyes of an orator have amagnetic influence upon the rapt hearerswhom he addresses. And his voice is lessaudible when he is looking down at hismanuscript, because the sound directionnaturally changes.

These difficulties, it is maintained, areovercome by the new appliance. Themethod consists in the manuscript beingreflected into the direction of gaze of thespeaker. It appears between the speakerand the audience in a reflector which neitherhides him from the latter nor hinders himin any way. As a result, the manuscriptcan be read in the reflector without thelecturer having to turn his direction of gazeor speech from the audience during thewhole speech.

Eloquent ReflectionsAT this point the intelligent reader will

naturally object that a reflectedmanuscript would appear in reverse. He isquite correct : the words would run like,the writing Alice saw looking -glass.So, if there were only a single reflector, themanuscript would have to be written ortyped like Hebrew, the lines of which readfrom right to left, in the manner thatprinters set up type. To obviate this, theinventor suggests that, as an alternative tothe manuscript being a la mirror -writing,an auxiliary, reversing reflector may beinterposed.

And so with this apparatus the speakercan administer to the public powerfulreflections.

FountaimPen SealI T has been said that a bad workman

quarrels with his tools. But an efficienttool is a necessary factor in first-class work.For example, Robinson Crusoe, with crudeimplements, could not produce the finishedwork of the well-equipped craftsman. Thisis certainly true of the pen. Take care ofthe pens and the writing will take care ofitself, is a slogan which, if original, I presentto " His Nibs " the pen manufacturer.

An improved self -filling fountain pen ofthe piston type has recently been patented.It is characterised by a piston adapted toslide in the barrel of the pen with a closeand easy fit. Fluid tightness of the pistonis secured by means of a groove containingmercury. With such a seal, it is stated thata much greater suction is obtained with ashorter stroke than is the case with a pistonhaving the ordinary packing.

And so that tiny tubular pocket inkpothappily named the fountain pen, will notonly resemble the shape of the column of thethermometer, but will also contain thatsprightly metal commonly called quick-silver.

(Continued on page 92)


A STEAM -DRIVEN SPEEDBOAT

ANY ship, boat, or model movingthrough water has constantly to bedisplacing a certain mass of water

of the same weight as the model itself, andthe water has to fill in the subsequent void.To do this with the least expenditure ofenergy, it must do it as gently as possible.If it is not done gently, a wave is formedon either side, indicating that energy isbeing wasted in raising the water above itsnormal level. These 'waves cannot beeliminated entirely, but it is the businessof the naval architect lip reduce them toa minimum.

In addition to this displacement resistancethere is the resistance due to what isknown as skin friction per square foot ofwetted surface, and this resistance isproportional to the amount of wettedsurface. It varies with the nature of theskin, i.e the substance of which it is madeor with which it is coated. This resistancein the case of destroyers has been found tobe:

At 12 knotsAt 16At 20At 30 ..These figures are taken from a standard

work on marine engineering.

An Experiment with a Rotating DiscA gyroscopic disc (with a certain string

pull) was rotated for the and half minutesin air. With the same pull in water it spunfor ten seconds only. The disc was thencoated with a film of paraffin wax ; it then

80 per Cent.70 t)

Fig. 1 . -Aphotograph ofthe finishedmodel of thesteam -driven

speedboat

twenty-four to twenty-seven times itsbreadth. Water offers very little resistanceto bodies moving slowly through it, butthis resistance of inertia increases veryrapidly with the speed; at high speeds(above 16 knots) it behaves more likea solid than a liquid.

will always be much faster than the ordinaryboat of the same power, even allowing forthe power expended on dynamic support.Obtaining the Maximum Speed from a Boat

(1) The boat must be long in proportionto its breadth.

(2) It must be as light as possible, i.e.displacement must be at a minimum.

(3) Its shape must offer minimumresistance, i.e. it must have a sharp cuttingedge and a tapering form of stern to fill upthe void without turbidity.

(4) Its centre of gravity must be as lowas possible.

What type of boat best fulfils theseconditions ? In all probability (with the ex -

Many Interesting Experiments can be carried outwith this novel Speedboat, which incorporates a

number of ingenious features in Design

The advantage of the hydroplane overthe ordinary boat is greatly increasedspeed. In the boat, the power is employedin wave making and overcoming skinfriction. The hydroplane, when travellingat speed, may have its wetted surfacereduced by as much as two-thirds, leavingonly one-third to produce skin friction-the displacement resistance having lessenedin the same proportion. Thus, providedit registers sufficient speed, the hydroplane

li" 21" --->1<

WWI

- - PLAN48°

ELEVATION

14" - -

Fig. 2.-A plan and elevation of the sheer of the speedboat shown above

rotated for twenty seconds. This experi-ment shows in a very striking manner howgreat this resistance can be, and how it canbe lessened.

HydroplanesWhy are hydroplanes so much faster

than ordinary boats?A hydroplane, or skimmer, is so con-

structed that it lifts itself out of the waterwhen running, and actually displaces verymuch less water and has far less wettedsurface than when at rest. To enable theboat to lift from the water, it must havea speed of about 16 kr ots, and unless thisis the case this type of broad, flat-bottomedboat is not nearly so army to drive throughthe water as the long and narrow type-say, the racing eight--vhose length is from

STERN

eeption of No. 4) an eight -oared racing boat.This type of boat has, of course, a high

centre of gravity, and is balanced by thelong oars of the rowers, but there is an easymethod by which this can be overcome.

The Three ModelsThree types of boat are dealt with in

this article. The ,smallest one is 3 ft. longand has a maximum width of 4 in.; acylindrical boiler, 12 in. long and 14 in. indiameter; a special vapour lamp (to bedescribed in detail later); and a StuartTurner " Meteor " engine. It is carefully" lagged " to prevent steam condensation.

The torpedo -shaped body beneath is thekeel, and all three models have such keels.

The long, narrow model is 5 ft. long and3 in. maximum width. The plan, orhorizontal section, is that of a racing eight.

The third model has a maximum widthof 54 in. and is 4 ft. long. It has a boiler,1 ft. long and 2 in. in diameter; a Whitneyengine, 4 in. bore and ft in. stroke double-acting; and also a Stuart Turner lubricatorand steam tap.

Fig. 3.-A close-up view of the engine of the steam -driven model


The long, narrow model is electricallydriven by means of two 4 -volt accumulatorsand an 8 -pole motor geared down about1 to 6.

The idea underlying the design of thesekeels is to lower the centre of gravity thenecessary amount-on the principle of thelever-with the minimum of weight, a 1 -lb.weight 4 in. below boat bottom beingequivalent to 4 lb. 1 in. below it. Theirtorpedo shapes offer minimum resistance.Results

Let us take the electrically driven modelfirst. Various motors were tried and various 9°.dry cells. Finally the plant described abovewas installed. Unfortunately this was veryheavy-each accumulator weighed 1 lb.and the motor 14 lb. -34 lb. in all. Thebalancing -keel weight was lb., and hadto be placed 64 in. below the boat. Thehull weighed 4 lb., and the result was thatthe boat was too deeply immersed for goodresults. Nevertheless, with freshly chargedaccumulators, using 8 volts, and favourableconditions, a speed of between 6 and 7 milesper hour was obtained.

The smaller of the steam -driven models,at a steam pressure of 80 to 100 lb., wascapable of a speed of 8 to 9 miles an hour.This model, although not so deeply im-mersed as the long electric one, obviouslysuffered from an insufficient floatationalcapacity. The larger steam -driven modelwas capable of practically the same speedas the smaller, at a pressure from 60 to80 lb. per square inch.

Its general behaviour was, moreover, farG

4".

O 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0

lc

0 0 0 0 0 0

O 0 0 0 0 0

o 0 0 0

o o 10 o

1

33/4o o o io o

O o 0 o o

MOLE FOR SAFETY VALVE 1 M5iCUT-OUT PORTION FOR STEAM OWE I

I1STEAM PIPE 6 PIPE TO PRESSURE GAUGE1

.1

F -4 Fig. 5.-Constructicnal details of the casing of the boiler M

superior to the smaller one. So far as isknown, these speeds are in excess of any-thing hitherto reached with a similar typeof plant and size of boat.

Constructional Details of the HullsIn the case of the steam -driven models

the bottom is a piece of ordinary 4 -in.three-ply, cut to the shape shown in Fig. 2.The sides are h -in. three-ply, glued andfastened to the bottom with small gimppins. At the bow and stern, V-shapedpieces of wood are fitted, to which thebottom and sides are glued and pinned.Round the top of the sides, from end toend, a strip of 4 -in. three-ply, 4 in. broad,is fastened. The hull is further strengthenedby one or two transverse pieces of L-shapedtin fastened to the sides. The hulls weregiven three coats of varnish and two ofaluminium paint. Paraffin wax was run'

--NEARLY 374. -----

FRONTHOLDER.

REAR.HOLDER

Fig. 4 . -Details of thetwo side platesof the boiler

round the inside edges and V-shaped piecesat the prow and stern to make themthoroughly watertight.

The hull of the long electrical model hada backbone or keel of wood, 5 ft. long with

tapering ends, 4 in.broad and 4 in. deep.To this was fastenedribs cut from 4 in.three-ply, and the shellwas of three-ply, if in.thick. A piece of 4 -in.three-ply, in. deep,was fitted to the top, oneach side, from end to

R end. V-shaped pieceswere placed at prow andstern. In every caseV-shaped pieces of tincapped the bow andstern to give a knife-edge.Boats constructed asabove are much strongerthan would be supposed.The Torpkdo Keel

Having decided on theweight to be used, apiece of thin brass tubingshould be cut and filledwith molten lead (ex-cepting in. at eitherend). Three small holesare drilled very near thetwo ends of the tube,

having equal circumferential differences, andinto these are fitted suitable turned or shapedpieces of wood to give the tapering forms at

A SECOND LAMP

VAPOUR CHAMBER

FINE HOLES FORFULL LENGTH OF LAMP

SECT ION OFFIRST LAMP

N

prow and stern. Screws through the holes a.,described above fix them to the tubing.

In the case of the electrically -drivenmodel the tube was 4 in. in diameter, totallength 9 in., distance from bottom of boat64 in., and weight lb.

In the smaller steam -driven model thetube was 84 in. long and 4 in. in diameter;distance below boat 84 in., length .7 in.,weight 4 lb.

For the larger model the tube diameteris I in., total length 7 in., distance belowboat 7 in. and the weight, 1 lb. Froma minimum resistance -point of view the -first has the best proportions.

The Power Plant and LampAfter considerable experimenting, two

lamps of different design were constructed,both of which gave very good results. Thefirst lamp, however, did not give quite solow a centre of gravity for the boiler, wasnot so easy to start, but had the advantageof simplicity. A vertical section of the lampis shown in Fig. 6, and its construction isquite simple.

Obtain a piece of thin tin, 114 in. by24 in., and bend a piece of thin sheetcopper to the shape and dimensions shownin Fig. 6. Solder the two edges of the latterto the edges of the strip of tin (note thecentral rectangular portion must not quitetouch the tin) and solder two rectangularstrips of tin, one at each end, to the centralrectangular portions of the copper, Makethe joints fluid -tight, and then solder apiece of thicker copper over each end,having previously drilled two small holes,one at each end in the bottom of thecopper. When spirit is poured into thecentral trough it will run through andpartly fill the entire chamber. A numberof small holes are drilled from end to endon the upper outside edge of the trough,and when the spirit in the trough is ignitedthe copper, a good conductor, is soon heated.Spirit vapour is thus formed, and, issuingfrom the holes, at once ignites. This lampis to be preferred to any form of wick lampand gives a far more intense heat. Owingto the narrowness and depth of the trough,the spirit is troublesome to ignite (especiallyin cold weather) unless it is poured in hot.It is heated by standing the container inboiling or very hot water.

The second lamp is shown pictorially inFig. 6. It contains three distinct parts: anordinary spirit lamp with wick, E ; achamber, F, in which spirit is boiled andevaporated, and from which a pipe leadsto a piece of brass or copper tubing ofrectangular 4 -in. section, closed at both ends.This tubing rests on the bottom of the boat,thereby giving the lowest possible centreof gravity for the boiler. In the top of thistube is drilled a large number of holes(fifty to sixty in number), using a 69- to75 -twist drill. They commence at A andcontinue to B, as shown. This lamp givesa steadier flame than the previous one, and

AIR -TIGHT R iNG CAP

VAPOUR TUBE

FILLER

WICK TUBE

AIR VEN117,--

thanFig. 6.-The construction of the two types of vapour lamp


can also be regulated by the flame of theheating lamp. It has only one disadvantage,however, for if the heating lamp wick isblown out it very quickly ceases to function.With this lamp, when once started, 6 oz.of cold water has been raised to a steampressure of 60 lb. in ninety seconds. Itgenerates steam sufficiently fast to keep upthe pressure for the " Meteor " engine andfor the larger f in. bore and stroke, thepressure falling very slowly with bothengines going all out, and using a 2 -in.propeller in both cases. The tins used forthe lamps were made out of lower parts ofold fruit tins, and only soft soldering wasused throughout.

The dimensions of the various parts areas follows : For the larger model (see Fig. 6),the container, E, is 3 in. in diameter, 1 in.deep ; container, F, 3 in. in diameter, If in.deep, and for the smaller model, E, 2 in.by ftin.,F,24in.by1l4in.

The actual amount of spirit to put ineach is best found out by a few experiments,but E needs but little, and should not goon heating F after all the spirit is evaporated.There is very little actual pressure and nosafety valve is needed ; soft soldering alonewill answer-but silver soldering makes thebest job.

The BoilerThis must be brazed. Obtain a piece of

copper or brass tubing of about 18 gaugeand of a suitable length. Blanks arerequired for the ends, a heavier gaugeshould be used for these, say 16, or even 14.

To provide the dry steam you must havea steam dome and a safety valve. Theycan be bought from 3d. up to 5s. 6d. and itis certainly advisable to use a good one.The same hole into which this screws is,of course, used to fill the boiler, which shouldbe filled not more than two-thirds full.A 2 -in. boiler, 12 in. long, holds 16 oz. ofwater. A pressure gauge is essential andif using a vertical engine it is essential touse a lubricator.

To mount the boiler cut two pieces ofthin tin to the dimensions shown in Fig. 4,and bend as shown. The 2 -in. hole can becut with an ordinary 2 -in. centre bit.They are then placed one at each end of theboiler, allowing about in. to protrude.They should be a good fit, their upturnedportions being screwed to the bottom ofthe boat.The Casing or Cover

This is of thin tin cut to the dimensionsshown in Fig. 5 and bent to shape. It is

essential to line the sides with thin sheetasbestos inside. A similar sheet of asbestosis placed on the top of the boiler-slightlycurved and with the necessary holes forthe safety valve, etc. Any additionalcorner or end pieces of tin that may benecessary to thoroughly shut in the flamemust be fastened on with very small nutsand bolts ; soldering is useless.

The safety valve (if spring is external)must be protected from the flame or itstemper may be spoilt. Asbestos -lined capsshould be fitted over the ends of the boilerto prevent radiation.

To obtain the best results, careful laggingof the pipe conveying steam from the boilerto the engine and of the engine itself isessential. To do this, place pieces ofasbestos in a saucepan containing a smallamount of water and boil, at the sametime pounding the asbestos to a pulp.Now squeeze it in a cloth and apply roundthe pipe, etc., afterwards binding with tape.The slide valve and cylinder of the engineshould be siniilarly treated.

The boiler and container F, especiallythe bottom, soon become coated with adeposit of carbon-a powerful non-conduc-tor of heat ; therefore they must befrequently cleaned.

OUR BUSY INVENTORS(Continued from page 89)

Accommodating Legowear A Wooden HatA SWISS citizen has applied for a patentrl in this country for an invention relat-ing to trousers. The specification describinghis device states quaintly that it is meantfor " sports people," i.e. cyclists, mountainclimbers, gymnasts, walkers, etc., whopossess both long and short trousers. Itadds that there are " sports people " who,for financial reasons, can acquire only oneof these two kinds of trousers. The inventorprovides trousers which will play the role ofboth the abbreviated and the elongatedvariety of nether garments. The legs aredivided, and can, consequently, be used asshorts. But, if desired, an additional lengthmay be affixed. The connecting means maybe slide fasteners or hooks and eyes.

Station IndicatorCOME time ago I stressed in theseJ columns the desirability of an indicatorin railway coaches to inform the travellerat what point the train had arrived. Therehas now been patented in the United States astation indicator comprising a movableweb having thereon the names of thestations in the order in which they appear.An electric motor causes this indicator tofunction. It should relieve the oft -puzzledpassenger from the necessity of picking outthe name of his destination amid the crowdof advertisements which surround it.

Streamlined TurkeysCHRISTMAS is coming. The season is

festive but, from the point of view ofthe turkey, it is tragic. It seems that thefull-sized bird is too huge for many smallovens. To overcome this difficulty, I learnfrom an American source, that, instead ofseeking an expanding oven to suit the vary-ing dimensions of the turkey, it is the aim ofcertain breeders to produce a bird of lessample proportions. The object is to caterfor families which are not so large as thatof the lady whose residence was a shoe.

THEpresent year is the centenary of the

death of William Murdoch, the inventorof gas for illuminating purposes. Afterarriving in England from Scotland, wherehe was born, he altered the spelling of hisname from Murdoch to Murdock on accountof the inability of Englishmen to give it thetrue guttural pronunciation. In his earlydays Murdoch, in the course of an interviewwith a prospective employer, owing to ner-vousness, dropped his hat upon the floor.The peculiar sound made by the fall excitedthe curiosity of the gentleman he was inter-viewing. Murdoch then revealed the factthat the hat was made of wood. He hadturned it on a lathe of his own making. But,although his hat was made of wood, hishead was not composed of that material,for his ingenuity conceived many valuableinventions.

* * * *

Tilley ProductsNOW

that restrictions have been placedon electricity and coal, the Tilley

paraffin radiator will prove ideal for warm-ing small rooms and is especially usefulwhere heat is only temporarily required.As it is portable and independent ofconnections, it can readily be moved fromroom to room, and being a radiant heater,its effect is felt immediately. It will give sixhours' heat for one penny per burner, andthe container holds sufficient paraffin forten burning hours. The radiator is 17 in.high, has a 124 -in. reflector and weighs34 lb. It costs 37s. 6d. If you require alarger size of heater, there is the Tilleytwo -burner radiator costing 72s. 6d.

This firm also have a large range ofparaffin lamps, an interesting line being thestorm lantern at 36s. It is strongly madewith no parts to rust or corrode. burnssteadily, and is unaffected by weatherhowever severe. The burner hood hasa small reflector which prevents rain fallingon the globe.

A Watch "Putand Take"

THE materials required for making thissimple device are a cheap watch, a sheet

of thin notepaper, and some water colours.Remove the back of the watch and care-fully remove the escapement (see Fig. 1).This will allow the hands to spin roundwhen the watch is wound up. Next removethe front of the watch, take off the hands,and remove the dial. A circle should thenbe cut from the notepaper (the size of thiscircle being effected in accordance with thesize of the original dial, and ruled off intoeight sections as shown. These sectionsshould then he coloured and the printing

A novel game made from an old watch

done in accordance with the illustration.P represents the word " put " and T" take." Res. means " re -spin " and T. Allbeing " take all." It is advisable topaint the sections up to the dotted line asin Fig. 2, the reason being apparent onreferring to Fig. 3. Now stick the paperdisc on the front of the watch (after makinga small hole for the hand " drive "), replacethe minute hand only, and finally the casing.

Should the watch have an unbreakablecelluloid cover (not glass), this will be anasset, since by slight pressure of the thumb(to prevent the hand turning), a good windcan be affected and consequently a goodspin attained on removing the thumb.


11 QUERIEScviaENQUIRIES

l

->U\ANL/

A Special Enamelis possible to make an enamel capableI of resisting the action of sulphuric acid,and would this need any special under-coat if used on wood?-N. J. (Essex).

UNFORTUNATELY, you do not sayto what strength of sulphuric acid

you wish your enamc coatings to beresisting. It is impossible to obtain anenamel which will resist the action orconcentrated sulphuric acid over ,ongperiods, but with sulphuric acids of ,owerstrengths (say up to thirty per cent. oreven more) any enamel containing bitumenwill be sufficiently resisting. You canprepare such enamel by making up astrong solution of bitumen in turps and byadding it to any ready -prepared enamel insuch quantity that it does not thin downthe latter too drastically. The woodworkshould be given three or tour coats of thisenamel, each coat being allowed to drythoroughly before applying the next.

Anti -sulphuric enamel of this typeis a commercial commodity and may beObtained from the leading photographicsupply houses, as, fOr instance, Messrs.Jonathan Fallowfield, Ltd., 61-62, NewmanStreet, London, W.I. or from Messrs. Mayand Baker. Ltd.. Battersea.

The enamel prepared as above will notneed any special under -coating, althougha preliminary thin coat of priming paintwill do the woodwork no harm.

We would warn you not to expect toomuch of these anti -acid enamels. They are,of course, quite satisfactory for diluteacids, but strong mineral acids quicklyattack them.

Zinc Oxide Adhesive Plaster

WHATis the recipe for the zinc oxide

adhesive plaster used on surgical tape?-K. A. (Middlesex).YOU can make zinc oxide plaster for

spreading on tape in two ways :-(a) Make up a mixture of olive oil and

zinc oxide, employing somewhat more oliveoil than zinc oxide. Allow it to standovernight and then heat it on a waterbath for two hours. On cooling, it will setto a white adhesive mass.

(b) Dissolve 1 oz. of powdered Castlesoap in 20 ounces of water and add thisto a moderately strong solution on zincsulphate. A white precipitate, consistingmainly of zinc oleate will be formed. Thisshould be filtered off, washed with coldwater and allowed to dry. It can be spreadon tape and will retain its adhesive condi-tion indefinitely.

Remember, when spreading the plastermaterial on the tape, that only the thinnestpossible layer of it is required.

A Direct Explosion PumpI HAVE designed and built a direct explosion

pump to work on coal gas, but so far Ihave not met with any success as I could

stamped addressed enve.ope, hree penny;tamps, and the query coupon trom the currentissue, which appears on page iii of cover, must beenclosed with every letter containing a query.Every query and drawing which is sent must bearthe name and address of the sender. Send yourqueries to ..he Editor, PRACTICAL MECHANICS.Geo. Newnes, Ltd., Tower House, South mpton

Street Str:nd, London. W C.2

not get the gas to ignite. i am using thehot -tube principle for ignition and the gasis at atmospheric pressure. I am certainthat once I can get an explosion, the valveI have designed for controlling ignitionand inlet gas will work.

Could you suggest any reason why thegas does not explode, or any other means 01ignition? --G. G. (Hull).

THElailure ol the gas to explode In

your pump must be due to one (orboth) of two reasons: viz.-the gas -airmixture may not be of the correct propor-tions and the ignition tube which you areginploying may not be hot enough.

For an effective coal -gas explosion yourequire a mixture containing about twelveparts of air to' one part of coat gas. if themixture is too rich in coal gas or toodeficient in it. it will not fire. Also, theignition tube must be heated to a brightcherry -red heat. Preferably, it should bemade of nickel alloy, or, better still, ofplatinum, which enormously facilitates theready ignition of the mixture.

Without being acquainted with the designof your engine, it is practically impossiblefor us to offer detailed suggestions concern-ing it, but we incline to the opinion thatyou would have more success .with it, ifyou could discard the hot -tube method ofignition and rely upon electrical ignitionby means of a spark derived from aninduction coil or a high-tension magneto.Possibly; though. you may have veryspecial reasons for sticking to the hot -tubemethod of ignition.

In general, however, provided t at yourgaseous charges have an approximatelycorrect composition and, also, providedthat your ignition tube is maintained at aufficiently high temperature, you should

IMPORTANT NOTICEOwing to the restriction of paper

supplies in war time, readers mayfind it impossible to get " PracticalMechanics " each month unless theygive their newsagent a regular orderfor their favourite magazine, now.

Wastage of surplus copies in theshops must be avoided, and readerscan be of the very greatest help if theywill fill up the Order Form given onpage 88 and deliver it to their usualnewsagent or bookstall. An order ofthis sort ensures regular deliveryduring War time, and the Editorasks every reader to help in this way.

PLEASE ORDER " PRACTICALMECHANICS " NOW AND USETHE ORDER FORM ON PAGE 88

certainly experience no difficulty in gettingthe gas to explode.

Colouring ConcreteI HAVE some pure white cement which 1

wish to tint blue and grey. Can you tellme of a non -fading blue or grey pigment touse?-E. H. (Bucks.)YOU do not mention the exact purpose for

which you wish to use the colouredoncrete. Hence, we cannot advise youupon the precise details of its mixing.However, an average mixing of dry Portlandcement and fine sand (approximately equalproportions of each) may be coloured byincorporating with it a suitable insolublepigment in amount proportional to thedepth of colour required.

For black or grey colourations, ordinaryiampblack mixed with a little finely.powdered pyrolusite or manganese dioxidewill give the effect' required, this pigmentbeing absolutely permanent.

The most permanent blue pigment whichyou can employ is Cobalt blue, which ha. arather greenish shade and which is expen-sive. Ultramarine is a good blue, but is notresistant against water, containing tracesof acids. Lime blue is a cheap pigmentand may suit your needs. None of theseblues, of course, possesses the same degreeof permanence to light and other influencesas common lampblack, and for use as aconcrete pigment in an exposed positionwe should say that an absolutely permanentblue does not exist.

" Carblyst'I UNDERSTAND that a " catalyst " is a

metal that has the power of assistingother chemicals to interact, merely by theirpresence, without entering into the reactionthemselves. Is this correct ?

Assuming that the above is right, couldyou give me a list of metals that have" catalytic " properties ?

Could you give me an address or addresseswhere I could obtain such metals ?-F. M.(Hants).

ACATALYST " is 'a substance, no,necessarily, but usually, a metal in

" finely -divided " or powder form, whichinitiates or accelerates a chemical reactiot,but, so far as we can tell, does not its.')actually take place in the reaction. Yost,definition of " catalyst " (whieh, incidentally, is itself a pretty meaningless word) c.correct.

As a typical example of a catalyst, let ustake platinum, in finely -divided form.When oxygen and sulphur dioxide areheated, they do not combine. When. hom.ever, these gases are passed over heatedplatinum. in it finely -divided form, theycombine almost completely, forming sulphurtrioxide. which can afterwards be combinedwith water to form sulphuric acid. This isa very important example of catalyticaction and forms the basis of the present-day " contact process " for the manufactureof sulphuric acid. Note, however, that ironoxide has a similar catalytic effect and hencethat a catalyst deed not necessarily be ametal.

The metals which are most used onaccount of their catalytic properties areplatinum, palladium, tungsten, mercury,iron, nickel, vanadium. All these areemployed in " finely -divided " form. Well-known non-metallic catalysts are iron oxide,nickel oxide,- ammonium vanadate, man-ganese oxide, manganese sulphate.

You can obtain any of the above materials(to order) from your local branch of Bootsthe Chemists or from a chemical supply firm


At a time like this we are onlyadvertising immediately usefulitems. Previous adverts. detailed

a wide range of goods. Where stock is limited preferenceis now given to National Service users.

ELECTRIC SUPPLY. An Independent Emergency orStand-by set may be of great value to you. Can betransported on any car that can carry 3 cwt. All thesesets that we are offering are in first-class order andstraight from reserve Govt. Stores, kept unused asstand-by. Being a pre -crisis release they are an oppor-tunity for a low price purchase that might not otherwisehave occurred and certainly cannot be repeated. TheHalf Kilowatt Set is worth £50, but our price is only tit,and with engine and dynamo carry the full Electradixguarantee.A.R.P. PETROL ELECTRIC GENERATING SETS for

Lighting and Charging. Half h.p. DIRECTCOUPLED 150 watts D.C., 1,800 r.p.m.,

2 -stroke water-cooled 1-cyl.Engine, magneto ignition. Onbedplate with 30 volts 5 ampsDynamo, 112.80 larger size t kW. S.T. PetrolElectric Sets, 500 watts, 2 -strokewater-cooled 1 h.p. 1-cyl. engine

on bedplate direct coupled to 50170 volts 10 amps. D.C.Dynamo, magneto Ignition, fuel and oil tank, tie.STORAGE. You may have charging facilities and wantto install high capacity steel accumulators which willhold their charge almost indefinitely.A.R.P. EDISON HIGH CAPACITY STEEL CELLS athalf price for stand-by lighting, 120 A.H. to 300 A. H. at20/- to 25/-. Makers' price is £5. Ask for leaflet. FULLPARTICULARS gladly given as far as we are able toA.R.P. ENQUIRIES.YOU MUST KEEP YOUR BATTERY PREPARED ! ! !

Battery Charging on A.C. Mains. The A.G. NITN-DAYwill keep your battery fit without attention. ModelN/A0, 100/250 volts A.C. and D.C. 6/8 volts t amp.,15/, Model 11 / BO, 100/250 volts to D.C. 6/8 volts I amp.,25/, Model N/CO3 100[250 volts to D.C., 6/8 volts 2amp., 35/-. Model N/011, 100/250 volts to 12 volts Iamp., 32/.. Ditto, 12 volts 2 amps., with 6 -volt tap,55/-. 5 amp., 114/101-.Fuggy Dugouts or Ill -ventilated shelters must be kept

A.R.P. SHELTER Ventilation and Air Condffroning.fresh.

Compact unit, drive off A.C. or D.C. mains, 80 watts;9 in. Blower, 20 cub. ft. fresh air per min. 25/- is abargain pricq.WET WEATHER ELECTRIC PUMPS, for A.C. or D.012 v. to 230 v. Centrifugal all -bronze pump, throws 120.gals. per hour, 72/8. Type R pumps. Twin piston typefor draining shelters, dug -outs, etc., 318/17/11.RADIO SIGNAL PHONES. Complete sets with 5 line or20 line exchanges. Portable army wardens' phones, etc.State wants.

POCKET HEADPHONES. W.D. all leather, headband strap and cords, 2/6 pair. Wireless

type with aluminium headbands, 2/9. 4,000ohms., Ct. LISTENING MIKES, steel -cladElectradix, indestructible; are ears outside

your dug -out.CABLE. Lightweight twin field cable, unbreakableArmy steel reinforced, 66/- mile. Heavier types,65/- and 70/-.FIRE CONTROL SIGNALS. Emergency day Lucas andAldis Hooded Army Signal Lamps, telescopic sights,hand or tripod. For Fire Brigades and Police, 60/-.AID RAID SIGNAL BELLS -FIRE ALARM BELLS.Waterproof mains, Battery or Hand magneto Buzzers;Morse Practice Sets. Morse Keys. Recorder gear, asprevious adverts.CRYSTAL SETS. Model B, Pol. Mahog. case, 9 in. by10 in., 2 tuning condensers, plug-in coils, PermanentDetector, 7/6. 4,000 ohms. 'Phones, 4/6.CRYSTALS, RECEIVING. Super Detector, glass cover,fine adjustment, 10/-. Enclosed 2 -crystal permanentDetector, 2/-. Carborundum Marconi Army Detector,2/6. Galena point Detector, mounted, 1/8. Galena andNeutron Crystals, 4d., 6d., and Perikon, 1'-. arborun-dum mounted, 8d.CRYSTAL OR BATTERY SET BUILDERS. FittedTable Cabinets, polished oak, 131 in. by 7i in. by 6 in.,oval aluminium black panel fitted geared, .0005-mfd.,sunk dial, 3 -way coil switch and a single plate verniercondenser, and 10 terminal Strip, new stock, 15/,MORSE PRACTICE SETS, No. 3, with key buzzer andlamp for sound and visual, line plug, etc., 7/-. SoundType, 1A type key and buzzer, 3/-. Visual Type 2A,

key and lamp, 2/-. Buzzers from 1/- each.KEYS. Govt.surplus table Morse Keys. Type

RBSL. Polished woodbase, massive brasspivot bar, tungstenspring-mountedeontactsfor quiet working andbase lamplor light. Afirst-class Key for opera-tors.

6'. EMERGENCY PARCELS of usefulstand-by electrical and radio repair materialand apparatus, 10 lbs. for 5/-. Post Free. \IDon't forget to send now for our Bargain List P.

ELECTRADIX RADIOS218, UPPER THAMES STREET, LONDON, E.C.4

Telephone Central 4611

ELECTRADIXTHE WAR

such as Messrs. Harrington Bros., Ltd.,City Road, London, E.C.

D.C. Motors on A.C.IS it possible to run a 200 volt, 0.5 amp,J continuous current motor on a 240 voltalternating current circuit?

I understand that A.C. can be used todrive ordinary D.C. motors so long as theyare not very large. My attempt to do sowith a motor of the specification given abovehas, however, proved unsuccessful. It maybe that the motor itself is faulty. -H. W.(Bethnal Green).

WHETHER a direct current motorwill run on alternating current depends

upon the type of winding. A series -woundcommutator -type direct current motor willoperate on A.C. fairly well, but will notdevelop the same amount of power, and thespeed characteristic will be much steeper,that is the speed will fall off more rapidlywith increase of load than when used onD.C. Also it is essential that both fieldsand armature should be laminated, other-wise considerable overheating is likely.With a shunt wound D.C. motor, however,the case is different. Since the armatureand the field circuits are independent ofone another and the self induction of thefield winding far greater than that of thearmature, the lag in magnetisation of thefields is so considerable that armature andfield currents do not arrive at their maxi-mum value at the same time, one beingnear zero value while the other is at maxi-mum, consequently there is little or notorque.

Wind Motor for Fountainintend to erect a wind pump for theI

purpose of pumping water up into atank of 28 gallons capacity and 9 ft. inheight.

The wheel consists of twelve vanes,each having an area of 15 square in. andbeing included to the plane of motion atan angle of 35 degrees. The total diameterof the wheel is 30 in. and it will be 9 ft. high.The water from the tank will be used to worka small fountain. Could you let me knowthe following :-

1. What size pump (single acting) this millwould work ?

2. Whether this size pump will keep thetank supplied with water? -H. G. (Don-caster).IT is always difficult to estimate the

power available from windmills of thetype shown in your drawing, not onlybecause of the variable nature of the windvelocity but also on account of the suita-bility of the site chosen and presence ofany deflecting obstructions. One cannotexpect very much from a wind vane 30inches in diameter on a tower only 9 ft.high, but the nearest estimate that can begiven as to the pumping capacity assuminga moderate wind velocity of 20 miles perhour with a pump of 2 in. bore and 4 -in.stroke would be approximately 60 gallonsper hour. Whether this would keep your28 -gallon tank fully supplied dependsentirely upon the discharge rate from thefountain jet, a matter for experimentalone. According to " Molesworth," acircular vane -type mill of 12 ft. diameterworking in a wind velocity of 15 miles perhour would only develop h.p., and onthe assumption that the power developedis approximately proportional to the squareof the respective diameters of the wheelsthe ratio would be 144 to 6.25, indicatingthat the maximum output from your30 -inch mill would only amount to a trifleover one hundredth horsepower.

INSTRUMENT WillaAt Half Ordinary Prime

Price per lb. for Double Cotton Covered25 SWG 1/8 28 SWG 2/2 30 SWG 2/1032 SWG 3/4 34 SWG 3/IS 36 SWG 4/9

Price per lb. for Double Silk Covered26 SWG 2/8 28 SWG 2/10 30 SWG 3/232 SWG 3/8 34 SWG 4/8 40 SWG 9/ -

Postage 6d. Reels and Winding 6d. per reelSPLIT PHASE A1 -4C2.5 MOTORS

All voltages.Ideal for workshop andindustrial uses. Heavy dutyrating. No radio interfer-ence and silent. I h.p. 55/-;t h.p. 65/, Other motorsfrom 16/6. Universal, Cap-acitor, Repulsion, at lowprices. Low voltage Trans-pfoinrgmsemj4ecoon= ta6/pi.

LLeaflets

Post 6d.L. WILKINSON, 204 LOWER ADDISCOMBE ROAD, CROYDON

In WORKSHOP and HOMEkeep warm with a PORTABLE

TILLEY RADIATORThe unpleasant conditions of winterare soon forgotten amidst thecomforts of the home. The TilleyRadiator being PORTABLE, pro-vides warmth in workshop, sitting -room, bedroom, bathroom, etc.,as required. Burns ordinaryparaffin at the low cost of Id.for 6 hours. Requires no con-nections or fixing. Absolutely safe.No wick to adjust and causesneither smoke, smell nor mess.British throughout. Price 37.6.Sold by all good Ironmongers andStores. If any difficulty, write to:-

TILLEY LAMP CO. (Dept. P.M.), HENDON, N.W.4

CHEMISTRY EXPERIMENTSFOR BLACK -OUT EVENINGS

BECK

Post Free OFFEROF SAMPLE PARCELcontaining manyuseful pieces of

CHEMICALAPPARATUS

2/9Write also forPRICE LISTof other Sets.

(Scientific Dept. A), 60, High St.,Stoke Newington, London, N.16.

Rpokiet, "Experiments in Chemistry," 6d. P.O.

BARGAIN OFFER

CHARGE YOUR L.T.AT HOME Battery ..1311ex"Charger

Just plug-in, fit spades, switch on, that's all!Prices : 2v., 1 amp, 12/6; 2 amps, 18/6; 6v., 1 amp,15/, Car Battery Models : 6v., 2 amps, 25/-;12v., 30/, Commercial Charger for 1-14, 2v.cells, 0-3 ammeter, Low, Medium, High taps, 50/-.Larger Models, 75/-, 90/-. All have Metal Rectifiersand strong steel cases. Send 3d. for REAL PHOTOand FREE TRIAL terms.

BRIGHTON RADIO SERVICE,34 Middle Street, Brighton.

Ilwiteglam,Imo' r

Easily made from ourcastings 12/6 per set.Complete Enginesready to run fromNM.

HALLAM & SONUpton, Poole,

DorsetitlIASH Vat. rasscut. ENGINES . . . forAet °planes and Speed Boats. 1 to 15 c.o.

Send 3d. for particulars


GREAT NEW TECHNICAL PART WORK

FIRSTPARTS.Now on

Sale AEROPLANEMAINTENANUEOPE

Every young man beginning a careerin aeronautics or changing over frommotor engineering should be certain

to buy it to -day !

THIS authoritative new part work is compiled underthe supervision of technical experts in close touch

with the very latest aviation practice in England andAmerica. It is absolutely comprehensive and ofinvaluable assistance to GROUND ENGINEERS,INSTRUCTORS, AIRCRAFT MECHANICS,AIRCRAFT ELECTRICIANS, and all whoselivelihood is wrapped -up in aeronautics.

Every detail of repair and overhaul, dismantling,inspection and reassembling is covered. Whetherthe subject on which you require technical andtrustworthy information deals with boost control,hydromatic air screws, ignition screening, latestde-icing equipment, operation and servicing ofaccessories and instruments, you will find it inAEROPLANE MAINTENANCE & OPERATION

A Brief Outline of the Important Contents:AERO ENGINE CARBURETTORS.

Principles of Carburation. Automatic Boost Control. The Hobson AVT9.5.MB Carburettor. The Hobson AV70-M Carburettor. S.U. Carbu-rettors. Rolls-Royce Carburettors. Zenith Aero Engine Carburettor-. etc.All the above will be dealt with from the point of view of operation. main-tenance. tuning, adjustments and repair

ENGINE STARTING EQUIPMENT.AERO ENGINE MAGNETOS..

AIRCRAFT ELECTRICAL EQUIPMENT.Electrical Equipment for opirating Wag Flaps and UndercarriagesElectrical Speed Indicators. Electrically, Driven Fuel Pumps and VacuumPumps. Rotax Weston Engine Indicating Equipment. Electric Genera-tors. Electrical Fuel Contents Gauge Navigation and Cabin LampsIgnition Screening for arm e -eines

AERO ENGINE DATA SHEETS.It is hoped in this series to cover most of the Engines given in the list be owReaders will, however, appreciate that this list may be subject to modifi-cation, should official requirements necessitate this.

Gipsy XII, Gipsy VI, Series I and II, Gipsy Major, Series 1, GipsyMinor, Hercules, Taurus, Perseus, Kestrel, Dagger, Cheetah Genet.Lynx, Leonides, Pelides, Rapier, Cirrus. Mikron Peregrine. AeroncaTiger.

VARIABLE PITCH AIRSCREWS.UNDERCARRIAGES AND TAIL UNITS.

Landing Legs. Lockheed Airdrauiic. Vickers Oleo Pneumatic. TurnerOleo Pneumatic. Dowty Oleo Pneumatic and Hydraulic. AeroplaneWheels and Brakes-Dunlop-Palmer. Dowty Hydraulic Brake Cont.ol.Pneumatic Brake Controls. Undercarriages. Dowry and LockheedRetractable Systems. Turner Olaer System. Tail Wheel Units Nutcracker Retractable Struts. Bendix Pneudraulic Shock Atsorber

AIRCRAFT 'CONTROLS.Controls for Wing Flaps and Undercarriages. Lockheed HydraulicControl System. Dowty Hydraulic Control System. " Messier "Hydraulic Control System. Dowty Hydraulic Accumulator-Rudder BarDifferential Control System Sperry Gvropilot-P.B. Deviator-SmithAutomatic Pilot.

INSTRUMENTS AND ACCESSORY EQUIPMENT.AEROPLANE WIRELESS EQUIPMENT

DE-ICING EQUIPMENT.THE LINK INSTRUMENT AND RADIO PILOT

TRAINER, etc.

N

WEEKLYPARTS

ATITO BE COMPLETED IN ABOUT 40 WEEKLY PARTS

CE

Jr AEROPLANEPART

MAINTENANCE&OPERATIONA COMPREHENSIVE WORK INTENDED FOR ALLINTERESTED IN CIVIL OR MILITARY AIRCRAFT

DEALING WITH

SERVICING,MAINTENANCE,and REPAIR of

LEADING BRITISHAND AMERICAN

AIRCRAFT andAERO ENGINECOMPONENTS

GIVEN IN THIS PART

DATA SHEETGIPSY XII ENGINE

GEORGE NEWNES

FREE Each part throughout the work will conta nan Engine Maintenance Data Chart. With

Part t a Data Sheet is presented dealing with the famousGipsy XII Engine.

Over 1,000 specially approved -action"photographs of operations and drawings,

also invaluable tables and data. etc.*

GET YOUR COPIES TO -DAYOf all Newsagents and Bookstalls.

George Newnes, Ltd.


AUTHORITATIVE

TRAINING

in WartimeIn peace -time the T.I.G.B. home -study coursesprovided first-class technical education. Forseveral years past the pass percentage ofT.I.G.B. Students at Professional EngineeringExaminations such as A.M.Inst.C.E.,A.M.I.Mech.E., A.M.I.E.E., A.F.R.Ae.S.,C. and G., etc., has not once been lower than96%-and no fewer than 22 FIRST PLACEShave been gained. In War -time the advantagesof T.I.G.B. Training-free from black -out andtravel difficulties-are most marked. To -day,The T.I.G.B. courses are the ideal method ofqualifying quickly for the great range of postsbeing offered by Industry and the Govern-ment to technically trained engineers, theneed for whom needs no over -stressing. WriteTO -DAY for "The Engineer's Guide toSuccess," containing the world's widest choiceof engineering courses covering all branches andrecognised qualifications. Mention branch, postor qualification that interests you. TheT.I.G.B. guaranteestraining until success-ful for the one fee.

The TechnologicalInstitute ofGreat Britain218 Temple Bar HouseLondon - - E.C.4

(Founded 1917)20,007 Successes

An Absorbing Hobby3UILDING A STUART MODEL ISAN ENGROSSING PASTIME, ANDTHE RESULT A CONTINUOUS

PLEASURE

We illus;rate.

STUART

NO. 10.High Speed

Steam Engine.

Bore 1".Stroke r.Each set is qu.tecomplete-drawings andinstruct:ons areincluded.

If you have a lathe-The rough castings -

If not-Fully machined set -

Ditto, with all holes drillddand tapped - - - -

8/6

18/6

25' -

This and many other Stuart engines arefully described in the 72 -page CATA-

LOGUE No. 3, 6d. post free.

STUART TURNER LTD.HENLEY - ON -THAMES

BUY, EXCHANGE or SELL

FREE SERVICE

FOR READERS

READERS requiring in-formation concerning

goods or services advertised inPRACTICAL MECHANICSshould give names of Adver-tisers from whom particularsare desired. Any number ofnames may be included andwe will obtain for you cata-logues, lists, and any otherinformation you may be want-ing. THERE IS NO CHARGEFOR THIS SERVICE.

Readers desiring particulars from anumber of Advertisers will, by thismethod, save time and postage. If anyAdvertiser stipulates that stamps orpostal orders are necessary beforesamples or catalogue are sent, pleaseenclose the necessary amount withyour instructions. You are cordiallyinvited to make full use of this Service.

ADVERT. SERVICE DEPT.,PRACTICAL MECHANICS,

TOWER HOUSE, SOUTHAMPTONSTREET, STRAND, W.C.2

Please obtain and send to me par-ticulars from the Advertisers in

your November issue whose namesI give on list attached.

Advertiser I Page No. I Information Required

Attach sheet of paper, with par-ticulars, and your name and address(written in BLOCK letters), withdate, to this announcement.

TOOLS-Continued

120 Combined Engineers & Woodworkers Vices, amost useful tool in any workshop, 6" Jaws, opens 4r.Clearance price, 4/9 each; honestly worth double.-Below.

500 Woolworker: Vices, 4" Jaws, clear 2/9 each.-Below.

85 Machine Vices for Drilling or Milling Machine.Robust design, Width of Jaws Of", opens ilf" verycheap to clear, 3/3 each, below.

2/9 any lot. Eight lots St -BelowToolholder with four H.S. Tools.

I" Adj. Boring Tool with H.S. Tool.i" Drill Chuck, taper or straight shank.-i" to " Silver Steel, 1:1 pieces, 13" long.f" to f" Silver Steel, 4 Ili., 2" to 4" long.500 Ass. Brass and Steel Screws. etc.100 Steel Hex. Bolts and Nuts, i" to i".16 H.S. Drills, 1 3.2" to 5/32".Slitting Saws, Ike 1'32" to A" thick, 1" hole.Two dozen Fine and Odd Thread Taps, to I".Three dozen Tungsten Hack -Saws, to 12".18 Grinding Wheels, 1" to 1" diam.Three H.S. Tap Fluting Cutters, 11" diam.One dozen Ass. Fees, 4" to 12".Dozen Toolmaker's Needle Files, indispensable.Best Carborundum Wheel, 7" by j" by f" hole.200 Springs I, al Trox. 6" long.Four Ass. Carborundum Wheals, to 31" diam., f" hole.Doz. Emery Wheels, -111- to f" thick. r hole.0" to 1" Adjustable Tap Wrench. Burke.-Below.12 Sets Stocks and Dies, eta, {u Split Dies, cutting 3/32".

At", 5/32", 136", 7/32", 1 , -ea', Whit. or B.S.F. or 0, 1, 2,3, 4, 5, 6. B.A. Complete with Taper Taps, Adjust-able Tap Wrench and Die -Stock, Seven Dies andTaps, usual price of these sets is 12/6, clear whilestocks lasts at 6/6 per set, extra sets of Taps, Secondsor Plugs, 1/9 set of seven.-Burke.

Small Taps, 7, 8, 9, 10, 12 B.A.; -11," Whit. 6d. each.No dies these sizes.-Burke.1" Round Dieu, Screwing .1" 156"; II": 4"; I" Whit.,

B.S.F.; or Brass. 26 'Threads; or American FineS.A.E. for Yankee Cars, Set of Five Dies 2/9 ; FourSets 10/- ; Best Quality 1" Die -Stocks, all Steel un-breakable with Hardened adjusting Screws, 1/9 each-Below.

4,000 Taps, Taper, 2nd or Plug, same sizes andthreads as Dies, 2;9 set, flair sets 10/ -.-Below.

Yea Blocks and Clamps, Starret pattern. accurate,first-class finish, 4/- pair.-Below.£1 orders carriage paid, except abroad.J. BURKE, 30 TRIPPET LANE, SHEFFIELD, 1.

31 in. WINFIELDi OR VALUE AND RELIABILITY

As illustrated E110 - 10 - 0or by 0 monthly payments of 18'4

3 in. B.G.S.C. Lathes from E4 - 10 - 0

The Winfield Mfg. Co.`12NeGSEA7aiks

BLUSFREE to all sufferers, particulars of a

proved home treatment thatquickly removes all embarrassment, and per-manently cures blushing and flushing of the faceand neck. Enclose stamp to pay postage toMr. M. Temple (Specialist), " Commerce House,"72 Oxford Street, W.I. (Est. 38 years.)

GRINDING AND POLISHING UNITI/10th H.P., A.C.-D.C., 100or 250 Volts, 5,000 r.p.m.Fitted with 4in. Mop. 3in.Grinding Wheel, Guardand Tool Rest. Built-inSwitch and 4 feet ofE3//6Flexible Cable. Price

EASCO 18 P.M., Brixton 111.11.1:i,Lundr,,S.W.9

BUY, EXCHANGE OR SELLAdvertisements are accepted for these columns at 3d. per word (minimum 12 words at 3s.-advertisements of less than 12 words aracharged at the minimum rate of 3s.) subject to a discount of 24% for 6 consecutive monthly insertions or 5% for 12 consecutive monthlyinsertions. TERMS :-Cash with order. Cheques, Postal Orders, etc., should be made payable to George Newnes, Ltd. The Proprietorsreserve the right to refuse or withdraw advertisements at their discretion. All advertisements must be received on or before the 5th of themonth preceding date of publication and should be addressed to the Advertisement Manager, " Practical Mechanics," George Newnes

Ltd.. Tower House, Southampton Street, Strand, W.C.2.

BATTERY CHARGING PLANTNO INCREASE IN PRICES while stocks last; see

Displayed Advertisement. Brighton Radio Service, 34Middle Street, Brighton.

CANOESBOAT AND CANOE. Kits irons 27/6. Also com-

pleted craft. Lists stamp. Winter reductions.-Metacraft (P), Christchurch, Hants.

CINEMATOGRAPHYART CINE FILMS. Exclusive 9.5 and 16 mm.

Cine Bargains, all makes. State wants.-P. M. Dane,64 Stanley Street, Liverpool 1.

ELECTRICALAC/DC MOTORS, 1/12th to 1/8 h.p., from 10/..

Stamp particulars.-Brookes, Banners Street, Cradley,Staffs.

ENGINEERINGMETAL FOR THE MODEL ENGINEER

Sheet, Tube and Sections in Aluminium, Copper, Brass,etc. No quantity too small. Stamp for lists. TheUniversal Productions. Rigby Lane, Bromsgroye,Worcs.

METAL WORKMAKE METAL TOYS. Easy, profitable with

"Success" Moulds. List free. Complete trial mould1/6.-Lee's, 1 Birkin Avenue, Nottingham.

MICROSCOPY "THE MICROSCOPE AND ENTOMOLO-

GICAL MONTHLY."-The premier journal for allstudents of nature. 1/-, from newsagents, or 1/1 fromMicroscope, 20/21 Took's Court, London, E.C.4.

MONEY -MAKINGOPPORTUNITIES

SALES REPRESENTATIVE wanted, spare time;35s. weekly easily made.-Richfords, Ltd., 8a, SnowHill, London.

II SP1111

I;alterCsat 54

R 600

tto"Easily the Best SolderingFluid Obtainable." Thisstatement by a regular userof "BAKER'S" expresses thegeneral opinion of the Motorand Engineering Trades.Sold in bd., If- and 1/6 tins.

also in bulk.

SIeWM.BURNETTI CO. ( cot micial) LIMITEDGREAT WEST 50551SttWerito,1DIVIM

OUR ADVICE BUREAU

COUPONThis coupon is available until November 30th,1939,and must be attached to all letters containingqueries, togethrt with 3 penny stamps. A stamped

addressed envelope niust also bee closed.PRACTICAL MECHANICS, NOV., I

MODEL AIRCRAFTPETROL ENGINES complete, £2 15s. 6d. or ready

machined assembly kit, 39s. 6d. Timers, propellers,gas and rubber kits. List 11/21:I.-Lowe, 10 LindberghRoad, Bournemouth.

MODELSFOR TRIX RAILWAYS : special 4-4-0 Tank

Locomotives and Coaches. List 1 1/2d.- Below.PERFECT USED MODEL TRAIN BARGAINS.

Popular makes. Send 4Vgd. for our catalogue and savemoney.-Georges', 11, Friars Street, Ipswich.

MUSICAL INSTRUMENTSBAND GUIDE. Hints on the Bugle, Drum, Flute,

Staff Parade formation, etc. Free, post paid.-Potter's (Manufacturers), West Street, London, W.C.2

PATENTS AND INVENTIONSHAVE YOU a sound, practical invention for sale,

patented or unpatented? If so, write CharteredInstitute of American Inventors, Dept. 18-C, Washing-ton, D.C., U.S.A.

PHOTOGRAPHY£500 worth, good, cheap Photo Materials, Films,

Plates, Cards, Papers, Chemicals. Catalogue and4 Samples free.-Hackett's Works, July Road,Liverpool, 8.

DON'T TAKE RISKS. Good developers meangood results. Our reliable stock developers keep twelvemonths after mixing. Satisfaction certain to amateursand professionals. Best developers ever put on themarket. Make two pints strong developer. 6d. each6 for 2/3, 12 for 4/-. Post free.- Hackett's Works,July Road, Liverpool, 6.

PHOTOGRAPHIC MATERIALS. Plates, films,mounts, chemicals. Interesting money -saving listsfree.-" Kimber's," 105 Queens Road, Brighton.

SITUATIONS VACANTG.P.O. ENGINEERING DEPT. (no experience

required). Commencing £3113/0 per week. Age 18-23,Excellent prospects. Free details of Entrance Exam.from B.I.E.T. (Dept. 579), 17-19 Stratford Place,London, W.I.

PLEASANT EVENINGSAT THE PIANO

Think of the intense pleasure to your-self and friends in being able to playduring long evenings and dull Sun.days. LET ME teach YOU to playreally well so that you shall makethe piano sing-and read musicreadily at sight l BY POST, fromordinary Music, no freakish methods.

You shall quickly play Songs. Dances.Hymns, and Gems from the Great Mas-ters so that your friends will want youalways. I have taught over 51.000 adultpupils during 35 years, they were of allstages from Absolute beginners, whostarted without knowing a note, to quiteAdvanced Players. I taught them and I

CAN TEACH YOU. Send P.C. for freebook and advice. Say if Ad -

Moderate, Elemen-tory, or Beginner.

H. BECKERBritish by Ili and

Descent)(Dept. 1 5131, 6 9 , Hoot St., London, E.C.4

CUT THIS OUT-Practical Pen Coupon Value 3d.

Send five of these coupons with only 3/- (and 2d. stamp)direct to the Fleet Pen Co., 119, Fleet Street, E.C.4.By return you will receive a handsome lever self -tillingFLEET S.F. PEN with solid gold nib (tine, medium, orbroad), usually 10/8. Fleet price 4/3, or with 5 coupons`only 3/-. De Luxe Model, FLEET SELF -FILLER.2/- estra.

SITUATIONS VACANT-Cont.DRAUGHTSMEN. Numerous vacancies available

in Electrical, Mechanical, Aeronautical and otherBranches of Engineering. Buildirg, G.P.O., etc., formen age 17-40. Exp. unnecessary if willing to learn.Details of openings, salaries, prospects, etc., FREEfrom N.I.E. (Dept. 372), Staple Inn Buildings, W.C.1.

WATCHMAKINGWATCH & CLOCK REPAIRERS. Send 3d. for

complete list of material and tools.-Blakiston & Co.,Ainsdale, Southport.

MISCELLANEOUSBE TALLER I ! Extra inches count ! ! Details

6d. stamp.-Malcolm Ross, Height Specialist, Scar-borough.

TELESCOPES, MICROSCOPES, ScientificInstruments, etc. Send for lists. Sale or Exchange.-C. V. Bolton, F.S.M.C., 49a Leigh Road, Leigh, Lancs.

CASTING MOULDS for Lead Soldiers, Indians,Animals, etc. Sample mould, 2/9. Catalogue stamp.-Industries 2, Waldegrave Park, Twickenham.

WIRELESSCRYSTAL SETS KITS, complete, 4/6, post free.-W. J. Buckle, 63 Avenue Approach, Bury St.

Edmunds.

TOOLSBRAND NEW POWER TOOLS of quality.

10 -inch bandsaws, 54/-; Jigsaws, 22/6; Bench Drills,11/-; Circular Saws from 25/-; 3 -inch S.C. ToolroomLathes, from £4 5s. New 1 -inch chromium platedMicrometers, 12/6; Electric Drills, 37/6; Grinders.-John P. Steel, Bingley.

GRAYSON'S Glass -boring Outfits and Tube.Cutters avoid risk.-Below.Taps, Dies, Files, Chisels and Punches.

Best quality at keenest prices.-Grayson & Company,300 Campo Lane, Sheffield.

JUBILEE WORM DRIVEHOSE CLIPS

The long -life clip withthe ever -tight grip.

The Best KnownFor Radiator Joints,Mr, Oil, and WaterHose Joints.

We guarantee a TightJoint.

Stocked by all Garagesand Accessory Dealers

L. ROBINSON & CO.,25 London Chambers,GILLINGHAM, KENT.

The *ADEPTLATHE

f In. centres, tin. Se.tween centres.

With compound slide -rest 22/-, or with hand.

rest °MY. 13/6.Screw Tail Stork, 5'6

extra Poet 1-ADEPT' 21 in. INDEPENDENT 4 -JAW CHUCK,Price 13,-; Post gd. THE SUPER ADEPT,' 33',F. VV . PO RTA SS, VflRRt7 ii'

MAKE MORE MONEY£3 to £6 weekly can be earned at home in a wonder-ful business of your own. No matter where youlive you can commence to make money In yourspare or whole time. No risk, canvassing or exper-ience required. A wonderful opportunity for anyonewishing to add pounds to their income. Particulars,stamp.BALLARD. York House, 12 Hambrook Road.

LONDON. S.E.r..

All application* respecting Advertising in this Publication should be addressed to the AD VERTISEMENT MANAGER, GEORGE NEWNES LTD.Tower House, Southampton Street, Strand, London, W.C.2. Telephone Temple liar 436:

. .

GAMAGES

ELECTRIC FURNACESAn indispensable appliance wherehardening, tempering, annealing,brazing, soldering, or the melting ofsmall quantities of metal is carriedout,.The finest materials only are used inits construction and there is nothingliable to get out of order. Specifi-cation : Size, 7 in. long by 51 in. wideby et in. high; weight, 71 lb.;Chamber Capacity, 1 in. diameter by:1 in. long; Consumption,200 watts; Temperature,850 deg. C.-1560 deg. F.

Carriage 1/- England or Wales.

SWIVEL BASE VICEwith two Sets of Jaws

A strongly made vice, especiallysuitable for borne garages, workshopsetc. Steel -lined jaws and specialjaws to take pipes and rods. Widthof jaws, 4 ins..opening to maxi-mum of 5 in-.Weight complete.25 lb.Carriage, 1/- Eng-land or Wales.

166

BRITISH MADETHROUGHOUT

First Quality Heavyweight3in. SCREWCUTTING, BACK GEARED,GAP BED LATHES (Sliding, Milling, Surfacing)An opportunity to secure a high-grade lathe at a remarkablylow price. Be advised and order now while ample stocks are

available.SPECIFICATION:-

Exceptionally strong headstock with adjustable bearings.Heavy, solid bed ensures accurate work. Machine cutchange wheels for all English threads. Saddle and slidehave large bearing surfaces, and the tailstock is of rigiddesign. Swing, over saddle 41 in., over bed 6 in., overgap 8 in. Diameter of mandrel 2 in., mandrel nose 1 in.x 12 threads. Mandrel and tailstock bored 1 in. clear.Centres No. 1 Morse taper, leadscrew in. x 8 T.P.1. Conepulleys 31 in., 31 in., 21 in. x t in. Back gear ratio 30 to 20,distance between centres 12 in., overall length 27 in., weight52 lb. Complete with face plate and ten change wheels.

Carriage (outside our extensive delivery area) 316 extra England or Wales

OR DELIVERED ONFIRST OF SIX

MONTHLYPAYMENTS

OF

HEAVY DUTYAIR COMPRESSORSA first-class compressor at aa most competitive price.I in. bore, 11 in. stroke.Splash lubricated, sealedcrankcase. Diameter of fly-wheel 9 in. Weight 34 lb.

Carriage 63',/6 Eng-ian d or Alsolarger

t Pales and morepowerfulmodelwith 2 in.bore, 2 in.

stroke.£4.17.6or ElDeposit,Balancein SixMonthlyP a y -

men tsof 14'3

ELECTRIC SAWBENCH6 in. combination teeth saw, rise and falltable. Adjustable fence, adjustablemitre guide. Ball -bearing spindle anddust -proof housings. Motor is h.p.totally enclosed; dust -proof bearings (donot require lubricating for 2 years).Windings heavily impregnated withinsulating varnish and tested to with-stand 2,000 volts. 2,800 r.p.m. Internalcentrifugal starting switch. Size oftable top 12 in. by 10 in. Saw will cut11 in. by 51 in. Weight

2 yards cab tyre flex. £9.7.854 lb. Complete With

IOR 37/6 DEPOSIT, BALANCE epg /.1in 8 MONTHLY PAYMENTS of I

For 2 2 0 2 4 0volts A.G.only

Please confirmvoltage. ..

Carriage (outside our extensive delivery area) 3/- England or Wales.

6in. ENCLOSED eh p. ELECTRICDOUBLE GRINDERS

Heavily constructed, they are ideal for the workshopwhere grinding jobs constantly arise. Totallyenclosed. Ball bearings, Single-phase motor. 3,000r.p.m. Complete with Wheel Guards, Ii in. GrindingWheels. Weight 52 lb. For200/220 and 230/260 volts, L-5.19.6A.C. 50 cycles.

IOR24/6 DEPOSIT, BALANCE in 6 17/6 I

MONTHLY PAYMENTS ofCarriage (outside our extenove detztery area) zit, Engtana or Is ities.

Send for copies ofGamages ToolBargain Leafletsfor Metalworkersand Woodworkers

MAINSTRANSFORMERS

at a Remarkably Low PriceExceptionally robust constructionOperate on any 200-240 volt A.C.main, transforming to 6 volts, 3amps. Ideal for machine tool light-ing, driving models, garage inspec-tion lamps, and as a component forbattery chargers, eine pro-jector work, etc. Brandnew and guaranteed.Post 6d.

Make Money with one of theseELECTRIC ENGRAVERS

An efficient, reliable outfit which will markwrite, etch or engrave on any hard,hardened, or soft metal. Enables youto make money by engravingidentity discs, etc. Most use-ful for marking all tfiletyour small tools.Works off any 6 -volt accumulator. 396 Post free.

DELCO-REMYELECTRIC MOTORS

at a Substantial ReductionDesigned for heavy continuous use,they are equally satisfactory forrepeated intermittent work such asin refrigeration. No special switchis needed for starting, and the motorcan be operated by means of anordinary tumbler electric lightswitch. All brandnew.1/5 h.p. A.C. Cap-acitor start. 200/250volts. 50 cycles.Originally listed at 4/,Also D.C. motors as above. On,Assorted voltages 100 to 250, asvPlease state voltage when ordering.

Carriage (outside our extensivedelivery area) 116 England or 1tiales.

Heavy Duty Block TypeCONDENSERS

1 M.F.D. Capacity. Suitable forvoltages up to 1,000 A.C. or 2,000D.C. Tested to4,000 volts D.C.Dimensionsapproximately41 in. wide, 9in. overallheight, /- in.thick, Bakel t eease. 200 to becleared at anenormousreduction.

216Post 6d.

GAMAGES. HOLBORN, LONDON, E.C.1 Phone war order: liOLborn R4R4 Oily Branch. 107 Cheapside,

I ublished about the 30th of each month by GEORGE NEWNES, LIMITED, Tower House, Southampton Street, St and, London, W.C.2., and Printedin England by THE SUN ENGRAVING CO., LTD., London and Watford, Hens. Sole Agents for Australia and New Zealand-Gordon & Gotch, Ltd. Sole ,k,,nts

r 'south Africa-Central News Agency, Ltd. Subscription Rates: Inland and Abroad, 7s. 6d. per annum. Canada, 7s. per annum. Register.;fi at the G.P.O.fcs transmission by Canadian Magazine Post.

Documents

RADIO CONTROL OF MODEL AIRCRAFT