On the Dnel,opmenf of Hydrogen jrom ihe Anode. 269

The oxygen of the protoxides of the preceding analysis amountsto ] 2.842 per cent.; but it would be fallacious to form anyopinion as to the composition of the whole, 801008 as we are notacquainted with the constituent minerals that compose it....olleeting together into one view the preceding results, wehod-

4. Mineralogical Compon.tz�on of the Dhunmalla Meteon.le.

I Nickel-iron 8.42 flron ' 6.88^ ` ̀ "- '. .-.` 9 4 Kw Lj Nickel . ) .542. Profosulphuret of iron . 5.6) -8. Chrome-iron* . 4.164. Chrysolith (Peridot or olivine) 47'67

TrI ~~lI~~ ~inub ~ ublein n]uriatic}l86O____________4~

XXXIV. On the Dnelopmenl of Hydrogen from the Awde.By Professor W. BEETzt.

Ty a solution of an alkali or,an alkaline earth be decomposed between magnesium electrodes, the negative wire undergoes

no change either in appnranee or weight, whilst the positivewire is dissolved with simultaneous evolution of hydrogen. Thedevelopment of this gas under such circumstances was observedbyW6hler and Buff: in the ease of another metal, alumioium ;the process, however, was rendered more intricate by the pre-sence of a considerable quantity of silicon, and the consequent ,formation _of siliciuretted hydrogen. The greater simplicity ofthe action when magnesium is used recommends the employ-ment of this metal.for observaLions on this unusual electrolysis ;for by its means we may not only trace the causes which act inthis case, but likewise those influencing the phenomena observedwhen the terminals consist of aluminium wires.

The magnesium wire made use of in the following experi-ments was from the works of Johnson, Matthey, and Co., of

* The quantity of chrome found in this meteorite is unusually large,being reyresented by 2.84 per cent. of Cr.403, and by 4�16 per cent. ofFeO, Ors 03 ; yet it is not without precedent,for in the meteoric stone thatfell at Nobleborough, Maine. U.S.A., on the 7th of August, 1823, Web-ster found 4 per cent. of Cry 08.

t Translated by Dr. W. Flight from Poggendorffos Annalea hr Phys&ad Chemie, No. 1, 1866.

I Ann. der Chem. and Pharm. vol. dii. p. 218.

270 Prof. W. Boote affff ftftfff Dem&ywunf,qf

London. Unfortanately I maid not procure wire of an] otherthieknoaa than that of- a moderate-siaefdl knitting-needle, ommotro weighing 0.44 grm. When expfoaefd to tho action of thocurrent it wu uncommonly quickly dafnolved, so that I bad toconstruct a special voltameWr in order to maintain tho action fora sufficient length of time. Two bOlefff (a and b) were boredthrough the under surface of aglue yowl (see 6garfff), anddoeefd with tight-Ruing corks.A Mirna piece of caoatchouc Wu -firmly cemented on each of then.corks by mnna of gutW pore.ha,and on eachof these India-rubberplate. was fastened a fannel-chaffed cap (c and d). The Wires

Ce and f ) were posses throughtho corks and caoatchoac platen from below, so that the undersurface of the veaafal remained water-tight. Over Rho two funnelswere audiometers, held in their places by aapporta. A partitionof poroue ware (g) divides the veaael into two Cells. Tho poai-five vim ia quickly diaaolved, and to replace it u fast u sod,fresh vim ia pushed up from below. Were it not earroandedby the cap Cc) it would be immediately eaten through at the pointProjecting from the caoatchoac plate, where in fact the cur-rent in moat powerful. The piece than separated in carried awayby the gae, and the experiment nndered t;aeleaa for qaantitffttipurposes. If an experiment in to ho intenapted wiiboat leav-ing the Wires expoaed to the 'action of the electrolyte, they mastbe withdrawn, the edges of the boles in the cooRedone- pi&teaclosing tho opening. `

The gas from tho anode never ignited apontaneoaaly ; in facttbo magnesium contained so omni{ a trace` of ailiciam" that theformation of aiiiciarettfed hydrogen wan not to be expected. Ana-lyaia of the gm showed it to conaiat of hydrogen` alone. Theaccompanying phenomena at the poaitive wire, and Rho relativeqaantitiea of gas disengaged (mm the two poles, differed verygreatly according to the nature of the electrolytes used ; it wat;,however, in theae accompanying circamatancea that the cause oftho anomalous development-of ydrogen wan found.

For moat of my experiments I employed a solution of sul-phate of magnesium, because I thought by the nae of thin liquidthey would be Inst likely to be obscured by aecondary action.The action wan very similar to that which \abler ad Badobserved in the cue of alaminiam in a solution of its cblorido ;that ia to any, the poaitive wire wan simply diaaolved. I alwayenoticed, however, that as soon u tho wire Wu dippod in tbo

|[|81 ll

-' IIe -11|\ ll, I

Hy kqm kom the Anotfc. 271

liquid it became black, and, moreover, that sometimes smallparticles of this coating were thrown o5, rendering the solutionin the eudiometer over the anode turbid. But in this case aimthe ratio of the quantities of hydrogen at the two poles wu sonearly constant that this could warmly be looked upon u anaccidenWi coincidence. The subjoined Table contains the res,litsof wy determinations in seven series of experiments. Thocolumn headed Cu gives the weight in grammes of metal throwndown in a copper voltaWeter introduced into the circuit ; H _and H+ show the number of cubic centiWetres of hydrogen re.duced to Oo and 760 minims. pressure, nspectively developed atthe neptive and positive poles. The colnWns snperscribed Mgdenote the quantities of magnesinm equivalent, as the headingsshow, to the copper in the voltameter, to the hydrogen bt thenegative electrode, to the hydrogen st the positive electrode, andlastly to the sum of the two last mentioned, whilst the 6nalwlumn (Loss) gives the decrease in weight of the positive wireduring electrolysis.

It follows most nnequivocallyfrom this Table, that the loss inweight of magnesium is equivalent to the total hydrogen givenoff from both poles ; the precipitated copper of the voltameter,on the other hand, is only equal to the �hydrogen evolved fromthe cathode.

It is seen, moreover, by comparing the coluWna H+ andH_, that the quantity of hydrogen disengaged from the posi-

tive pole is nwewhat more than one-third of that given off fromthe negative wire. In experiments 8 and S this excess is greatest ;and as I wn especially struck with the larger quantity of blackincrnstation thrown off in these two experiments, rendering theliquid in the eudiometer particularly cloudy, it occuned to moto seek, in the presence of this black body, the mum of the snomelons development of hydrogen. I endeavoured, therefore, toisolate it, and succeeded to a certain oxtent in doing so. If ssolution of chloride of sodium be electrolysed betwan two mag-

--qIll

272 Prof. W. Beets on the Dmelopment of

Regina electrodes (the negative plate can be replaced by a pla-tinum electrode), a considerable quantity of black matter at oncedeposits on the positive pole. Part of this substance is sweptoff by the current of gas, part falls to the bottom. A gas is con-tinually being developed from this substance, even when it is nolonger in contact with the plate on which it was deposited.Collected in a eudiometer and analyzed, the gas proved to behydrogen. If during the electrolysis the endiometer be heldfirmly upon its caoutchouc plate so that none of the blackmatter can fall out, the current of course not being stopped,and if, lastly, the measuring of the gas-volumes, when the cum.enthas ceased, be delayed till there is no longer any gas disengagedfrom the precipitate, it is then found that the sum of the volumesof hydrogen evolved from the two poles is again equivalent tothe magnesium dissolved ; the ratio of the two gas-volumes,however, depends on the strength of the current.

In the two following experiments dilute solution of chlorideof sodium was detomposed in the usual manner ; in experiment8 six Grove's cells were used, and in experiment 9 the magne-sium wire which was to form the positive pole was directly fast-ened to the platinum wire as negative meWl.

No. E -.

8 14.99 8.78

The ratio of H- to H+ was likewise never more than 3 to1 when solution of chloride of ammonium was employed as elec-trolyte.

lo I 14.4 1 9.77 I 4.8 1 0.0151 I 0.0104 1 0.9958 | 0 098

In this cue no black precipitate was formed.If the black body produced by the electrolysis of a solution

of chloride of sodium be allowed to remain in the liquid, it issoon covered with white Hakes, and is dually converted into awhite muddy substance. This consists of hydrate of magnesia.If the Jiquid be greatly diluted before this change is complete,the black body can be perfectly purified by stirring the solutionbriskly and pouring off the lighter white Hakes. It undergoesbut little change in water ; by no method, however, hove Isucceeded in drying it unchanged : when under the receiver ofthe air-pump over sulphuric acid, as soon as it was nearly dry,it became grey, and a mixture of white and black particles could

Hydrogen from the Aso,fe. 273

then be clearly distinguished by a pocket-lens. Though I hadon this account to abandon analyzing this body, its nature couldbe infened from other circumstances. If the black precipitate,well washed, be placed in dilute acid, it dissolves with evolutionof "hydrogen. The solution contains no chlorine, so that it wasnot necessarily the electrolysis of a chlox'ide which had causedthe formation of this body ; it is moreover identical with the in-crustation formed in the solution of sulphate of magnesium. Asubstance which by decomposition of water and development ofhydxogen oxidizes to magnesia, could only be magnesium, or alower oxide of this metal, a&ozide of magneium. As the rela-tion between the amount of the body dissolved and the volumeof hydrogen generated could not be determined, this point couldnot be sealed by analytical means. But, apart fx'om the factthat no cause at all can be found why a separation of spongymagnesium should only take place at the positive pole, the pre-cipitate in its electrical comportment resembled an oxide. Ifthe current of a battery be passed through very dilute sulphuricacid between magnesium electrodes, the positive wire becomesimmediately black. If the two wires be now connected with sgalvanometer by muns of the reverser, the positive wire is Bratpositive and then.becomes immediately powerfully negative, re-maining so till the black incrustation has vanished. In anexperiment the image of the scale of my reflecting galvanometermoved ten divisions to the positive side, but with the next swingof the mirror went over to the fiftieth division on the negativeside, remained motionless there, and then went very&lowly backto zero, whilst the wire became Brat covered with white spotsand then entirely white. When I Brat ,observed this phenome-non I thought I had to dowith an action similar to that alreadynoticed in the case of iron*, to which I gave the name of " ano-malous polsrization," but which Wiedemannt bu called " posi-tive polarization." I soon- saw, however, that there were twodifferent things to be distinguished here-a polarization, and theelectromotive action of the black incrustation. The Brat de-flection, the positive, is to be ascribed to a polarization. Thisquickly vanishes, and is caused by the development of hydrogen ;for even in dilute acid hydrogen is evolved from the magnesiumanode during electrolysis. That the negative plate appears notto be the most strongly positively polarized, but the positiveplate covered with a negative layer of oxide, is not without pre-cedent ; for the negative body covered with hydrogen is oftenmore positive than the positive itself : for instance, platinum ina gas-battery, when covered with hydrogen, is more positive than

* Poggendorff s Sanalen, vol. Ixiii. p. 415.t Leke oom Galoaa ._us,vol. i. p. 508.

Phil. Mq. 8. 4. Vol. 82. No. 216. Oct. 1866. 7

274 Prof. W. Ileetz on the Dcoe&yJmenf of

wpper*. In any caee, however, the second dofleotion zhowztbet the black precipitate ie negative tovarde magnesium ; thenegative neture vaniehez with the black body it.If. The attnproceeding is moreover independent of the closing of the secon-dary bettery. If the battery..current be broken end munexionwith the gelvznometer be made only after the lap s of sometime, the blackened vim ie immediately negative ; if tho mzg-nesium wires be not connected with the inztrument till the blackinerusWtion ie gone, scarcely coy eleetrical difference iz thenobeerved between them. ginger experimentz can zleo bo madewith other conducting liquide ; tho proceu, however, iz moreintrinw end fumizhez no de6nite Faults, because hydraw ofmagneeie _ mzy be formed on both wires, which iz not poeziblewhen dilute aeide are employed.

The Bret idea which prezented itself with regard w tbo parti-cipetion of the zuboxide in the development of hydrogen wee,that the current only pertly decompoeed the zalW of tbo eolu-tione in the normal meaner, and partly the weter iteelf. If, forexemple, mH were given off from the eathode in a eolution ofchlorido of sodium, and pH from the enode, the quantity ofmagnnium dieeolved iz, eceordiog to the experimente dezcribod,= Cm +p)Mg. let the current so divide iteelf thet it deoom-pose s equivelente of veter, then mO end (m-m)CI will be mtfree. The latter combinee with (m - z) Mg, loving (p+m) Mg,which formz an oxide with zO. When this compound bu beenwmpletely oxidized w magnesia, it conWinz (p+m)MgO. Ifwe could deWrmino thie quantity experimentally, we ehould aleeknow m, the portion of the current thet decompozee water Iexamined therefore, &mt of ell, whether tho quantity of magnesiaformed in the nascent zWte, in a ult liquid holding ehloride ofmagnesium in eolution, wu considerable. 0.067 grm. of mag-Demon win, equivalent to 62.6 cubic centime. of hydrogen, weeplaced under a eudiometer in a solution of common salt whichhad frequently been used for olectrolyziz with megneeium, untilthe wire had crumbled Sway to a white powder. The liquid weefiltered off from the preciyitaW; the latter wu wuhed on thefilter, ma then dizeolved In dilute eulphuric acid. After caporating this liquid, 0.828 grm. of zulphete of megneziz remained,which is equivalent to 0.0656 grm. of magnezium, or 61'1 cubiocentime. of hydrogen. 62.5 cubic centima of hydrogen badbeen given off. It ie thue seen thet uo appreciable quzntity ofmagueeie bed been dieeolved.

8olution of chloride of sodium wee now deeompoeed betwanmagnesium electrodez, end, a&er the black precipitate bed beenconverted into. the white povder, tho ebove procezz repeated.

� Ba my own reeeerchu, w PoggendorS'z SaxaJelal. vol.Ixxvii. p. 504.

Hy6ogm }vow {he &odt. 275

Two experiments gave the following results :-Hydrogen. Sulphate of Hydmga.Found. ` magnesia. Calculated.89.9 0.209 89-0625.9 0.132 24.7

According to this, the quantity of sulphate of magneaia urnequivalent to the hydrogen evolved ; that in to say, p+s-p,and consequently s-0. The black precipitate was thereforenot produced by the action of the current, but by a purely chemical process.

The black incrustation DcV6rtheless required the agency of thecurrent for its formation. A bright magnesium wire, whenpieced in distilled water, is but feebly attacked ; aome hydrogenis developed, and a thin 6lm of hydrate of magnesia coven thewire, protecting it from further change. It Wu not noticed thatthis oxidation ia preceded by the formation of the auboxide. Ifthe part not immersed be touched by a platinum wire, whichlikewise dips into the acid, the magnesium then becomes black ;on stopping the current the incrustation dissolves. In a solu-tion of chloride of sodium a magnesium wire long retained itsmetallic lustre ; when touched with a platinum wire, u abovedescribed, it turns immediately black. Moreover, even withoutthe use of platinum, black spots farm on the wire, whence ablack incrustation sOOD 8pF6ad8 over its 6DtiF6 surface. A copiousquantity of hydrogen is now evolved from it. The But blackapot is due to local currents arising from small inequalities of thesurface as soon u the Brat spot is formed, local currents of greaterintensity are produced. But these currents do not, any momthan that of the batWry, decompose the water, but the Dalt in theaolution ; the part, therefore, which the current plays in theformation of the suboxide is no other than that of continuallyexposing fresh metallic surfaces to the action of the water.

The several phenomena which different salt aolutione presentare now easily to be explained. In chloride of ammonium, thenuboxide dissolves immediately on its formation, with evolutionof hydrogen, because magnesia is, u a rule, soluble in ammo-niacal salts. In solution of chloride of sodium it changes, with-out being dissolved, into hydrate of magnesia, because chlorideof magnesium forma no basic salt with magnesia. On the otherhand, it dissolves to a certain degree, and with evolution of hy-drogen, in aulphate of magnesium, because in this case a basicsalt ia generated. This basic componnd appears to be formedwhen H- : H+ as 8 : 1 ; hence we should be able to deduce thecomposition of this salt if that of the auboxide were known.

WShler and Buff ascribed the evolution of hydrogen from theT 2

276 Prof. W. Beets on Lke DmeLapmenf of

positive aluminium wire to the ready solubility of the ̀ basic chlo-ride of aluminium. This, though undoubtedly a true cause,is not the sole one. It is to be prnumed, from what bu gonebefore, that the development of hydrogen from the aluminiumand the magnesium bas a common origin ; besides, the positivealuminium wire also becomes black during electrolysis, and atthe end of the process continues to give off hydrogen, like themagnesium wire, only not so abundantly. All the eases of elec-trol.ysis examined by W6hler and Buff furnished a solution ofbasic chloride of aluminium ; and it never occurred to them toinvestigate uses of a different kind, their interest being concen-Lated on the formation of siliciuretted hydrogen. If in placeof a strong solution of ehloride of sodium a dilute one be em-ployed, the alumina is no longer completely soluble, and the ex-periment then bears a greater renmblance to that with magne-sium. The wire not only turns black, but the whole of the liquidin the audiometer becomes gray. A grey powder separates fromthe wire, and continues to evolve hydrogen after the electrolysisis interrupted. I have never seen it become entirely white. Ifwashed on a filter and treated with dilute bydrochloric acid, itcompletely dissolves ; it contained no silicium, or only triflingquantities, like the aluminium wire itself, which I obtained fromthe nme source n the magnesium wire used in the foregoingexperiments. The solution contained iron, however ; and to thisthe grey colour may possibly have been due. The electrolysisobserved by W6hler and Buff with concentrated solution of Chloride.of sodium between alumiaium wires conesponds thereforeentirely to that, examined by me, of solution of gulf hate of mag-nesium between magnesium electrodes ; we ought consequentlyto Bud also in the latter ease the nearly constant ratio of H_ : H + .

The electrolysis of dilute solution of common salt nolonger gavethis proportion ; on the eontrary, I invariably found the alumi-nium dissolved to be equivalent to twothirds of the quantity ofhydrogen given off from the two poles. . I believe, therefore,that in the case of aluminium also the formation of a suboxide'precedes the evolution of hydrogen. A peculiar circumstanceprevents the separation of this suboxide. On account of thesolubility of the basic chloride, no great quantity of the substancecould be obtained either from diluW solution of cbloride of sodiumor from dilute bydroehloric acid. In other salt solutions and indilute sulphuric acid, however, no evolution of hydrogen Wkesplace ; here, on the contrary, the phenomenon is that which bubeen already described by Buffs. The positive aluminium wirebecomes covered with a dark incrustation, which is stronglyelectro'negative and a very bad conductor ; it gives off a little

* Ana. cj!er Chm. uad Pharm. vol. CU. p. "269.

Hydrogcn !ram the Anode. 277

oxygen and no hydrogen ; the current is so weakened that it isnearly reduced to nil. Buff regarded this incrustation an sili-darn. The formation of a coating of silicium is undoubtedlyquite conceivable ; for our aluminium always contains some. Ihave, however, a reason for not regarding this Rim as silicium :pour some silicium powder into a glass tube the lower end ofwhich is closed with parchment paper ; dip this end into dilutesulphuric acid ; then place one aluminium wire in the acid andanother in the silicium, and in every case tbe silicium is foundto be pon.tire towards tbe aluminium. It matters not in thisexperiment which of the wires be first dipped in tbe solution,the aluminium wire immersed in tbe acid is invariably negative.If tbe current be weak on account of the bad conducting-powerof the silicium, it is only necessary to press the aluminium wirestrongly against the powder in order to bring its particles moreclosely in contact with one snotbcr-a method previously adoptedby me when using substances in a pulverized state*. The sili-cium which I employed was crystalline. Amorphous siliciumwas not readily procurable at the time, though I had a bodywhich comports itself in a precisely analogous manner-amor-phous boron. This body, when treated in the same manner withaluminium wires, was also distinctly positive. The badly-con-ducting .incrustation tbercfore could hardly be silicium ; I regardit, on the contrary, as a suboxide of aluminium. At all eventsthis suboxide is a very bad conductor, it consequently docs notgive rise to the formation of local currcnts ; and it does not dis-solve in dilute acids. If, on the other hand, from the possibilityof forming basic salts, it be predisposed to further oxidation, itgives x'ise to just tbe same phenomena as the suboxide of mag-nesium ; and consequently the explanation given by W6bler andBufF, for tbe only case which concerns us here, of the`anomalousformation of hydrogen is the correct one.

BufEt entertains the same view of the passive state of themetals which is upheld by me:. He Ands in a very insolublelayer of oxide or in a Rim of oxygen, protecting tbe metal from.further attack, the cause of the passive state. The formation ofa suboxide on the surface of a metal which is known to possessthe property of passivity to a high degree, appears to me to giveadditional support to this view.

Henrici found, in his experiments on the effect of motion ofmetallic wires in liquids, that aluminium comports itself in stotally diffc.rent way from other metals. In explanation of fillsanomalous bebaviour, he says " If it be assumed that tbe ala-

� Poggendortf'a Annalm, vol. exi, p. 619.t Ana. dev Chem. and Pharnr. voL eii. p. 265.: PoygendorH 's Annalen, vol. Ixvii. p. 186. Q ibid. vol. exxi.p. 496.

278 Prof. Challis on a Problem in

minium, covered as it is with a thin, insofuble, oxidized Rim,becomes negatively excited in the immediate region by the hy-drogen which is set free, whilst the,mm itself is preeminentlypositive towards the metallic surface that it overlies, then thephenomenon observed must undoubtedly anise its appearance."I believe that my experiments have justiRed this assumption.

XXXV. On a Problem in Ibe Calcufw of Variat ̀ sons, in reply toMt. Todhunter. By Professor CnALLXs, M.A., F.R.S.,F.R.A.S.*

T HAVE only a few concluding words to say respecting theL problem in the Calculus of Variations, the consideration ofwhich is resumed by Mr.` Todbunter in the 8eptember Number,the discussion of it having advanced to a stage at which, so far atleast as my views are concemed, a deRnite issue may be statedI have all along understood the problem to be that which Mr.Todbunter bas thus enunciated : To determine the greatest solidof revolution, the curt;l1ce of which is given, and which cuts theaxis at two Axed points. The generating line of the surface Isuppose to be subject also to the condition of being continuous,so far n not to change its direction per sallum. It bu beenshown in the course of this discussion that different lines fulfil-ling this condition, together with that of mtting the axis at thetwo points, give solids having the same superRciea but differentdegrees of magnitude. As these gradations cannot go on unli-mitedly, there must be a limiting or maximum solid the surfaceof which falsie the same conditions. It would be posaible bypractical tentative methods,'although it would be an unscientiRcproceeding, to mould a given quantity of matter into the requiredform. The maximum, therefore, exists s.n rerum nalurd ; and tothe discovery of its form by analysis all my efforts have been di-rected. I cannot tecognize as having any claim to be nlled thesolution of the problem a fotm which does not fulAl the aboveconditions.

la the July Number I have given two investigationnone de-pending on the equation Ap-0, and the other on A -0. Iahowed at the same time that the former equation could onlygive a line symmetrical with respect to the axis of revolution,and consequently, if any, only a conditional maximum, and thatthe absolute maximum must be deduced from the equation A = 0.Further, it was inferted from the radical involved in A (assumingalways that the function ot functions to be found admit of exactalgebraic expression), that the equation A =0 should be resolved

* Commumated by the Author.

8

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