22 RUSSELL-DETERhllh'A TION OF FUiIlIGclNTS. P.4 R T XI'lII J.S.C.I., 66, January, 1947

mixed glycerides containing both unsaturated C,, and unsatu- rated C,, acids. iMoreover, the observed maximum iodine value of 124 demands the presence of much mono-ethenoid unsatu- ration in the glycerides of the fraction concerned, as will be seen from the following calculated figures :

Iodine value Oleo-linoleo-erucin . . . . . . . . 108 '3

Dilinoleo-erucin . . . . . . . . 13 j '7 Linoleo-linoleno-erucin . . . . . . 163.2

Oleo-linolcno-eruciii .. .. .. 135'7

The manner in which oleic, linolcic and linolenic acids accompany each other throughout the mixed glycerides of the fat is further illustrated by the consistent and parallel increase in the proportion of each of these acids on passing from the least soluble fraction A to the mcst soluble fraction C of the rape oil glycerides (Table 111).

Consequently it can only be concluded that the unsaturated CIS and C,, acids (the major componcnts of the fat) are distri- buted very evenly amongst the glycerol molecules.

(b) The saturated acids-all very minor componcnts-will almost esclusively occur only once in any triglyceride molecule in which they may be present, i.e. they will occur in mono- saturated-di-unsaturated glycerides. In Tablc I\', for purposes of calculation, the further assumption has been made that this group consists wholly of (mono-saturated)-(mono-CIS-unsatu- rated)-(mono-C,,-unsaturated) glycerides ; but it is, of course, possible that simpler types may be present in small proportions, namely, some mono-saturated-di-C,,-unsaturated glycerides (especially in fraction A), and some mono-saturated-di-CIS- unsaturated glycerides (in fraction C). The amounts of these will hardly, however, be significant on the whole fat and in any case, the figure of about xSY0 (mol.) for the mono-saturated di-unsaturated group as a whole is probably near the truth. The remainder of the fat has been apportioned, in each fraction A, B, C, to mixtures of tri-unsaturated glycerides containing either one CIS- and two C,,-groups, or vice versa.

The rape oil thus contains, according to this study, about 24% of mono-" oleo "-di-" erucins," 2So/u of di-" oleo "-mono-

erucins," and xS0' of mono-saturated-mono-" oleo "-mono- " erucins " (where "oleo " and " erucin " signify respectively groups of unsaturated C,, or unsaturated C,, acids). These figures differ considerably from those of the earlier work'

mono-C,,-di-erucin, 507; di-C,,-mono-erucin and 6''; palmito-" oleo "-erucin), but the differences are wholly due to the altered data for the component acids obtained by the newer techniques in the course of the present work (vide itdra). In the earlier study, the amount of saturated acids detected was little over 276 (nearly all palmitic), whereas in the present investigation nearly 3y0 of palmitic acid and about the same total amount of other saturated acids was shown to be present in the mixed fatty acids of the rape oil ; calculated as mono- saturated glycerides in each case, the resulting values are respec- tively 6'jb and xS0,b .

It should be observed that (apart from quantitative data dependent upon the component acid figures) both studies (the former employing '' progressive hydrogenation," and the present relying upon preliminary resolution by fractional crystallisation) lend to the unequivocal conclusion that rape oil consists of a mixture of mixed glycerides assembled on the usual plan of pronounced " cven distribucion.''

Rape oil caniponent acids.-Application of low-temperature crystallisation in the quantitative determination of the component acids in each fraction A, B, C of the glycerides of the oil not only permitted the more certain definition, referred to above, of the minor amounts of saturated acids from myristic to lig- noceric, but (with the further aid of spectrographic analysis after alkali-isomerisation) established two- , further points of some interest :- ... ._

(a) The proportion of linolenic acid was shown to be con- siderably greater than that previously observed, with consider- able consequent alteration in the linoleic and (to a less extent) the oleic acid contents, whilst there was also evidence of traces of hexadecenoic acid.

(b) In the unsaturated C,? acids, erucic acid was found to be dccompanied by small but spectrographically significant proportions of a docosadienoic acid. In earlier work, the C,, ester-fractions from the 'I liquid " acid groups of rape oil acids had almost invariably possessed iodine values slightly in excess of that of methyl erucate, but these differences had been erro- neously attributed to imperfect separation of unsaturated C,, esters.

Consequently, the proportions of individual acids in the two analyses vary, sometimes considerably, although the totals for the various groups are less discrcpant (saturated 5 .9 (present) and 3 (former) ; unsaturated C,,, $2 :5 and 50 ; unsaturated C?,, 51.5 and 47?& mol.). There is little doubt that the data given in this papcr are closer to the proportions of the component acids actually present in the rape oil than those of the former study.

One of us (P. A. L.) is indebted to the French Scientific Mission to Great Britain for the opportunity to undertake this investigation at the University of Liverpool.

The Universiry, Liverpool

I<rccired July ' 5 . 19.16 Hilditch and Paul, J.S.C.I. 1.935, 54, 331T Hilditch, Alorton and Riley, Analyst, 193s. 70, 65

DETERMINATION OF FUMIGANTS. PART XVIII. DETERMINATION OF LOW CON-

CENTRATIONS OF METHYL BROMIDE By JOHX RUSSELL

This investigation was undertaken 10 develop a rapid method of determining small quantities of methyl bromide in gas samples collected during fumigation and airing. T h e vacuum flask trch- nique adapted to aralytic combustion of the methyl bromide has been used, and two methods of determination of the inorganic bromide formed have been tested. T h e Kolthoff-Yutzy method is suitahle but lengthy. A quicker electrometric mcthod has been evolved. The determination of methyl bromide is usually carried out

in two stages : first, the conversion of methyl bromide into inorganic bromide, and second, the determination of inorganic bromide.

Methyl bromide may be converted into inorganic bromide by hydrolysis or its equivalent, pyrolysis or catalytic combustion. Decomposition with ethanolamine and with sodium methoside are examples of the hydrolytic type of method. Williams and co-workers' have evolved a pyrolytic method in which air containing methyl bromide is mixed with hydrogen and passed through a quartz tube maintained at 800". The catalytic com- bustion of methyl bromide has been developed by Lubatti and Harrison.? The vacuum sampling flasks used in this method contain electrically heated platinum filaments, on the surface of which the methyl bromide is catalytically oxidised. Hydrogen peroxide and sodium hydroside. are introduced into the flask by cooling. In this way, the methyl bromide is quantitatively converted into sodium bromide. The pyrolytic and catalytic combustion methods can be applied to the determination of a greater number of volatile halogen compounds than the hydrolytic methods.

Lubatti and Harrison? determined the sodium bromide, formed in the catalytic combustion, by the methods of Mohr, and of Fajans and Wolf. These methods are accurate in the determination of quantities of inorganic bromide' not less than 1.0 mg. To determine lower concentrations, the author has

J.S.C.I., 66, January, 1947 RUSSELL- D ETERM INA TI0 N 0 F FUMIGANTS. P.4 R T X VIII 23

applied to the catalytic combustion technique the Kolthoff- Yutzy modification of van ter Meulen’s procedure? and an electrometric method. The Kolthoff-Yutzy method can be used in presence of large amounts of chloride, whereas the electrometric method gives better results when halides, other than bromide, are absent. The Kolthoff-Yutzy method has the disadvantage that it involves a number of lengthy operations. The electrometric method is accurate and rapid, although not specific for bromide. Sampling

In these esperinients, catalytic combustion flasks of varying volume wcre used, namely, goo ml., So ml., 30 ml. and 20 ml. The goo ml. flasks are mainly required for trace-concentrations of methyl bromide obtained during airing. At present, the So ml. flask is used for most general fumigation purposes and at concentrations above 10 mg. per litre, this gives the smallest amount which can be determined accurately, using the argenti- metric methods of Mohr or Fajans and Wolf. The increased accuracies of the Kolthoff-Yutzy procedure and the electro- metric method make it possible to use much smaller flasks. The smaller flasks (20 and 30 ml.) are especially useful in taking samples from the interstitial spaces of material undergoing fumigation, since taking large samples from these spaces may lead to serious errors:’ The 20 ml. flask differs from the 80 ml. flask described by Lubatti and Harrison’ in having the envelope in the shape of a test tube of about 2 cm. internal diameter. The goo ml. flask is constructed similarly, excepting that a B2.l joint is used instead of a B I ~ joint, and the capillary and filament are proportionately longer. The envelope has an internul diameter of 8 cm. Two methods of establishing known concen- trations of methyl bromide were used. A known volume of gaseous methyl bromide was measured in a micro-burette and transferred to 3 5 litre glass vessel provided with a stirrer. Alter- natively, a known weight of methyl bromide in a sealed ampoule was liberated in a 300 litre steel chamber provided with a fan. When necessary, an allowance was made for sorption on the walls of the container. Catalytic Oxidation

After catalytic oxidation, the Kolthoff-Yuwy method of estimating bromides has to be applied to alkaline solution containing a considerable quantity of hydrogen peroxide.

When determining bromide in solutions of potassium bromide, complete removal of hydrogen peroxide was found to be necessary. Platinum black and osmic acid removed the bulk of the hydrogen peroxide in a short time, but not the last traces. The best method of removal was by evaporation of the solution just to dryness. Prolonged heating causes appreciable errors due to decomposition of grease from the sampling flasks. The alkalinity of the solution from the sampling flask facilitates the elimination of hydrogen peroxide. Willard and Heyn5 have shown that the pI1 of the bromide solution before oxidation with hypochlorite must lie between 6.5 and 7.0, and that it is prefer- able to adjust it to 6.8. This has been confirmed and it has been shown further that before the addition of the buffer solution of sodium dihydrogen phosphate which establishes this pit , the solution must be slightly alkaline. In fact, in the catalytic combustion method the alkaline solution remaining after removal of hydrogen peroxide is suitable for the Koltho!l-Yutzy proce- dure. It is best to add the minimum amounts of hydrogen peroxide and sodium hydroxide whenever possible.

Lubatti and Harrison recommend, for samples containing 4-2 mg. methyl bromide, I ml. 100 vol. hydrogen peroxide and 2 ml. 0.5 N. sodium hydroxide. For samples containing 0 .1 mg. and less, 0.2 ml. peroxide and 0.5 ml. sodium hydroxide were found to be sufficient.

Proctdure. The combustion is carried out as previously described.? The total washings should be about 50 ml. In

general, to remove hydrogen peroxide, the solution is evaporated to dryness over a low flame or hot plate, with a watch glass over the mouth of the flask. With very low concentrations of methyl bromide, where only 0.2 ml. of 100 vol. hydrogen peroxide is used, it is sufficient to boil until the volume of the solution is reduced to about 10 ml. In the first case, the residue is redissolved in 10 ml. distilled water. Determination by Kolthoff-Yutzy method

Proccdiire. 2 ml. of 20% sodium dihydrogen phosphate solution and 2 ml. of the sodium hypochlorite-sodium hydroside solution are added to the solution remaining after catalytic oxidation. The solution is boiled far z minutes. 2 ml. of 5072 sodium formate solution are added to the boiling solution, and the solution boiled for a further 2 minutes. The solution is cooled to room temperature, and the volume made up to 50 ml. One drop of 5:; ammonium molybdate solution, 0 . 5 gm. potassium iodide and 25 ml. of 6 s. sulphuric acid are added. If any coloration is observed after the addition of potassium iodide, the sample is rejected. The titration is carried out with 0.01 N. sodium thiosulphate solution from a 2 ml. or 5 ml. microburette, graduated in 0.01 ml. I ml. of 5% starch solution is used as indicator. A blank esperiment is carried out on all reagents. I ml. of 0.01 N. sodium thiosulphate solutionfo.1583 mg. of hleBr. The reagents are those specified by Kolthoff and

A stock solution of sodium thiosulphate, 0.10 N., is made up. By diluting 10 nd. of this solution to 100 ml. in a standard flask, fresh 0.01 s. sodium thiosulphate solution is prepared for every series of determinations and is standardised against standard potassium iodate solution. All other reagents are of A.R. grade, except the sodium formate.

Restilk The results are shown in Table I. The practical limit of the results obtainable, has been taken 3s plus or minus twice the (percentage) standard deviation. The concentrations studied vary between 0.06 mg. per litre and 15 mg. per litre, and cover the range met in practice. The lowest are such as must be determined in the atmosphere during airing, those somewhat higher are such as are present in the intergranular spaces of foods, etc., from which only small samples tnay be taken, whilst the highest are those met with at the end of a normal fumigation. If the volume of the sampling flask is between 20 and 30 ml., the maximum percentage error is about 3 unless the concentration is very low. With 20 to 30 ml. flasks the error is about 7% if the concentration is 3 to 6 mg. per litre. With 900 ml. flasks and the very low concentrations of 0.05 to 0.06 mg. pe.r litre, the error rises to 14”/. The errors in mg. per litre corresponding to these percentages are, in every case, quite low enough for practical purposes. Determination by potentiometric method

The sodium bromide from the catalytic combustion is deter- mined by titration with dilute silver nitrate solution, the end point being determined potentionietrically. The electrode system is of the silver-silver bromide type, and utilises, instead of the usual calomel reference electrode, a “ bottled end-point ” silver-silver bromide electrode.0 A valve-voltmeter is used to amplify the changes in potential of the electrode system. This type of apparatus, although not so accurate as resistance-bridge types is more suitable for rapid analyses, as it gives continuous readings and is more readily portable. The method combines the rapidity of the argentimetric method with the accuracy of the Kolthoff-Yutzy method.

The valve-oolfriiefer. The valve-voltmeter is a simple direct- coupled amplifier (Fig. I). Two pentodes of thc type rCs-GT,!G are used to obtain the required amplification and to operate the circuit at very low voltages, thus making the amplifier portable. In general, this class of circuit is not practicable for amplifying changes in D.C. applied to the grid of the input valve, because

Yuay.3

Flask vol. (ml.1

900

80

80

80

30

30

20

20

RUSSELL - DETERMINA TI0 N 0 F FUA f IGA NTS. PART X V l l l J.S.C.I., 66, January, 1947

Actual conc.

per 1.) 0.060 0.060 0.060 0.045 0.045 0.045 0.568 0-568 0.568 0.568 0-568 0.568 I '422 1.383 1.345 I '309 1 '277

(me.

11 '20 10.70 10.26 9-842 9'471 9.103 11.36 10.89 10.45 10.06 11.30 11.1g 11.0g 10.87 19'23 19-05 3 '977 3'912 3'904 3'831 3'923 3-869 14-09 14-05 14.80 14.75 14.70 5'875 5'845

2'756 2.746 2.736

2'950

:A hiean recovery

;;:::] 98.33 102-13 i III'll

104.44 108 '89 I01 *78

99'81 99-16 I01 '39 99'79 I01 '59

98.85 96-79

99-01 IOO'IO

98.59

98.04 102.63 100 '52

100.79 100.38 100.86 99'70 99.651

1 100.47

99'55 99'46 I 0 0 '45 1 100'18

I:.% J 100. IC 1 104.68

100.03 100.57j 100.36 100.85

97'90

101.30 97'79 103.59 1oi.47 102 *g8 106-85 96.31

100'22

J

Stand devn.

0' I 0

7'04

1 - 1 1

1-74

I -32

I a46

2 .a8

1-14

3'90

of instability of the grid and plate circuit batteries, small changes in their potential causing false changes in the potential across the output resistance. This instability can be remedied by employing negative feed-back, Le., by introducing the output voltage of the amplifier into the input in such a manner that the net input grid-voltage and amplifier gain are reduced, thus ensuring greater stability.' There are some deviations from the normal direct-coupled amplifier circuit with negative feed-back. The pentodes have separate sources of high-tension so as to provide independent adjustment of grid and plate potentials. A milliammeter (0-1 ma.) is placed in the output circuit and is provided with a variable shunt to give an adjustable scale. The value of the negative feed-back resistance is 50 ohms.

The elecfrode ustern. The titration cell (Fig. 2) consists of a 100 ml. Pyrex beaker mouuted on a wooden turntable, which is driven, through a worm reduction gear, by a small D.C. electric motor with a rheostat in circuit to control the speed of stirring. The two electrodes, A and B, dip into this beaker and are supported by an adjustable wooden holder mounted on a vertical wooden rod, b e d to the base board. B is the indicator electrode

FIG. I

Index of cortrponeim (Fin. I) Acc. 2-volt accumulator BI 9-volt grid-bias battery B2 9-volt grid-bias banery tapped so that there is a potential of

1.5 volts between + and H.T. +, and 7.5 volts between H.T. + and H.T.-

C microfarad condenser MA RI 15,000 R resistance Rz 20,000 R variable resistance R3 Rq

% 3 resistance $ /Single pole toggle-switches

V2

Milliammeter ; scale 0-1 ma.

25,000 R variable (shunt) resistance 50 R (negative feed-back) resistance 10,000 R variable (biasing) resistance

I ICs GT/G pentode valves. Filament voltage I '4 volts.

and consists of a Pyrex tube 11 mm. outside diameter, drawn out to a little over I 111111. in diameter so that a silver wirc (I mm. dia.) can be sealed into it with " Picein " wax. The silver wire is soldered to a bakelite-mounted terminal at the top of the tube. The terminal is fixed to the glass by a layer of " Picein " wax. A is the reference electrode which consists of two parts. The upper part is a Pyrex tube sealed to a ground glass socket and carrying a silver wire and terminal similar to those in the indicator electrode. The lower part E of the electrode is a Pyrex tube connected to the upper part by a ground glass cone and closed at its lower end by a ground stopper to avoid diffusion of the electrolyte. When in use, the ground surfaces are wetted just enough to give electrical conduction. The lower part of the reference electrode is three-quarters filled with a suspension of silver bromide, prepared by taking equivalent quantities of o * m z ~ N. potassium bromide and 0.001 N. silver nitrate, and adding a very small excess of potassium bromide. The solution is then made decinormal with respect to potassium nitrate.

Procedure. The electrodes are connected by well insulated wires to the valve-voltmeter input terminals which are provided with a shorting switch. When the electrodes are not in circuit, and the shorting switch is open, there is a tendency for the terminals to collect stray charges j the grid of the first valve becomes so charged that, if the biasing potentiometer R5 (Fig. I) is arranged to give a reading of, say, 0.2 ma. when the shorting switch is closed, there will be a natural drift of the needle com- pletely off the scale. This property of the circuit is utilised as follows. The eIectrodes are arranged so that the natural tendency of the grid of the first valve to gain a charge is opposed. Thus when the electrodes are in circuit the reading should be near the extreme end of the scale. If this reading is off the scale, it can be brought back to some arbitrary point by means of the shunt, R3, across the ammeter. The zero should also be re- adjusted. Before each determination the cell circuit is shorted out. This is done by turning the biasing potentiometer, Rs, until the ammeter shows the desired reading. The reading is

J.S.C.I., 66, January, 1947 RUSSEL L-DETERMINA TION OF FUMIGANTS. PART X Vl l l 25

next taken with the cell in circuit and with the electrodes immersed in distilled water acidified with a few drops of 0.5 N. sulphuric acid. Sulphuric acid is used to increase the conducti- vity and because it is used in the actual neutralisation of alkali in determinations of methyl bromide. The reading is noted, as this will be the valuc of the anode current at the end point in the titration. This procedure is repeated after the titration, as there is a slight drift, although it is generally small enough to be neglected.

After catalytic combustion, the alkaline bromide solution transferred to the titration beaker, is neutralised with 0 .5 N. sulphuric acid, and some fked volume is added in excess (usually z drops). The indicator used is Neutral Red, which usually has been found to introduce no appreciable error. The beaker is replaced on the turntable and the electrodes immersed in the solution. Standard silver nitrate solution is slowly added from a micro-burette and the ammeter needle is allowed to come to a steady position after each addition. The beaker is rotated at a suitable speed to ensure efficient stirring. When the needle has almost reached the position obtained by immersing the electrodes in distillcd water, the succeeding positions of the needle, through and beyond that position, arc noted for each addition. This gives an accurate end point within 1% of the correct value in estimations of very small quantities of bromide (0.1 mg.) and gives no appreciable error with larger quantities (I mg.). However, if the greatest accuracy is required, the whole of the titration can be recorded and graphed, the end point being determined graphically. 0.001 .N. silver nitrate is used in the titration of amounts of less than 2 mg. bromide ; higher concen- trations are used for larger amounts.

Fig. 3 refers to a concentration of 8 * 5 mg. per litre determined by the electrometric method. A 20 (22.34) ml. sampling flask was used. In this figure the anode current is plotted against the volume of o a x N. silver nitrate added. By plotting the differ-

ential of this curve against the volume of silver nitrate added, the end-point can be calculated with great ac- curacy, I ml. of o*001o N. silver nitrate solution394.96 micrograms of methyl brom- ide.

Results. The results are shown in Table 11, and are calculated as in Table I.

FIG. 2

TAELE I1 EIecfrotttctric titerltod, rising o*001 N. Ag NO, sobirioti

Actual Conc. Flnsk cone. found vol. (mg. (mg. 7; M y (ml.) per 1.) per 1.) recovery ,"

1.436 1.414 1.392 1'979

1.843 2'099 2.058 2.039 2.007

1.639

I .621 2.883 2.873

2'599 2'7%

I I ' 20 11-16

11.08 11.04 39-10

20 { 11'12 38 *80 41 '70 41 ' 5 5 41 '39

40'94 40'79 40.64

1-486 103.48 1.450 102.55 1.442 103.59 1.931 97'58 1.878 100.48 1.831 99'35 1.996 95'09 z.054 99.6i 2.007 98.43 1.9~0 97.16 1'493 91-09 1.513 92.65

2782 96.50 2.816 98.02 2.938 102.62 2'730 98.03 2768 106.50

::g

2.695 104'09 11'10 99'1.1 II*OS 99'01 10.97 98.65 11'03 99'55 10.93 99'00 39-14 100'10 38% 99-13 38.24 98.56 41'99 100.70 42.38 102~00 41.38 99'98 40.56 98.71 39'93 97'53

39.38 96.90 40'14 98'41

99'54

99'97

99'75

93 -96

100.96

99.06

99'30

99.18

Using 0.02 N. AgNO, solution

16 I

ml. 0'001 N. rilvcr niirbtc

FIG. 3 Titration ciiwes

o*too O a5 1.5 z.0 2.3

ml. 0'001 N. rilvcr niirbtc

FIG. 3 Titration ciiwes

Stand dev.

or ,O

0.71

2.17

2.82

5 '23

4'03

0.36

0.79

1.81

26 lV00 DS-LIQ UID- VA PO U R EQ LllLlBRl,UM DA TA J.S.C.I., 66, January, 1947

The concentrations studied varied between 0. I and 40 mg. per lime. The high concentrations may be met with during fumiga- tion, and the lower are the smallest that can be conveniently determined by this method. In fumigation practice determination of lower concentrations is very seldom necessary. If, however, it were found necessary to determine less than 0.1 mg. per litre of methyl bromide in air, the following modifications to the method-would have to be made :-

(a) The final volume of solution to be titrated should be reduced by evaporation to io ml.

(6) Instead of the ordinary micro-burette, a Rehberg (or similar type) burette should be used for titration.8

The maximum percentage errors are about the same as those of the Kolthoff-Yutzy merhod. This method becomes inaccurate if any considerable proportion of other organic halides is present in the methyl bromide (as used for fumigation). In doubtful cases, results should be compared with those obtained by the Kolthoff-l'utzy method, and suitable modifications introduced where necessary.0,

This work has been undertaken on behalf of the Australian Dried Fruits Board.

Imperial College of Science and Technology, Department of Zoology and Applied Entomology,

Ind. Hng. Chem. (Anal.) 1945, 17,289 and 295

Ind. Ens. Chem. (Anal.) 1g37,9,75

Ind. Ens. Chem. (Anal.) 19~3~15, 321

South Kensington, S.W.7. Rcccivcd August 14, 1946

? J.S.C.I. 1944~63, 140

J.S.C.1. 1937, 56, 54T

a Pinkhof, Dissertation, Amsterdam, 19x9 ; Callan and Horrabin,

' Bninerd, Kochler, Rcich and Woodruff, " Ultra High Frequency Techniques " (Chapnian and Hall), p. IOI

a Rehberg, Biochem. J. 1225,19,270 Potcntiomctric Analysis," John Wile). and

Sons and Chapman and Ha11

LIQUID-VAPOUR EQUILIBRIUM DATA FOR THE SYSTEMS : METHYL METHACRY- LATE-METHANOL AND LMETHYL METHA-

By D. E. \\'OODS

J.S.C.1. 1928, 47, 329

Kolthoff and Furman, __

CRYLATE-METHACRYLIC ACID - Liquid-vapour equilibrium data for methyl methacrylate-methanol

and methyl mcthacxylate-methacrytic acid mixtures have been determined using a modified Rosanoff apparatus at 200 mm. and 760 mm. Hg Pressure. I t has been found that methyl mcthacrylate forms constant-boiling binary mixtures both with mcthanol and with water. Some physical properties of pure methyl methacrylate and mixtures with water, mcthanol and mcthncrylic acid have been deteMneiTJ In order to design a fractionating column to produce pure

methyl methacrylate, it became necessary to investigate the liquid-vapour equilibrium data for the systems methyl metha- crylatc-methanol and methyl methacrylate-methacrylic acid. T o compare the relative advantages of vacuum and ordinary pressure fractionation, the determinations were made at pressures of 200 and 760 mm. Hg. Some experiments were also carried out with mixtures of methyl methacrylate and methacrylic acid. The system methyl methacrylate-water was not investigated in detail, since it had previously been found that water present in the crude ester distils at 49" (zoo mm.) as a constant-boiling binary mixture with ester. Mixtures containing various per- 'centages of methyl methacrylate from o to IOO were made up from ester (prepared by the method described by Crawford' and purified by fractionation under reduced pressure), metha- crylic acid (similarly obtained from crude ester), and pure methanol. Determinations of the composition of the vapour in equilibrium with a given liquid mixture were carried out using a modified Rosanoff apparatus.' This comprised a cylindrical

glass vessel 3.*5 in. long by 1.5 in. diameter, of 60 ml. capacity, fitted with a capillary side tube for filling and a central delivery tube. The upper surface of the vessel and the upper end of the delivery tube were so shaped that any vapour condensing before entering the delivery tube fell into it and did not run back into the liquid, Le., the liquid was distilled with the minimum of rectification. The whole apparatus was immersed in a water- bath. The boiling points of the mixtures used were determined in an all-glass apparatus, comprising a cylindrical flask of 35 ml. capacity, fitted with a small reflux condenser and a thermometer. The apparatus and contents were heated.in a water-bath and the rate of refluxing ofthe boiling liquid increased until the tempera- ture reached a constant maximum value ; this was taken as the boiling point and was found to be reproducible to within 0-1'. The apparatus was previously calibrated using both methanol and water.

The refractive indices of the mixtures used were determined in an Abbe refractometer and the densities determined by pyknometer.

(a) MefhyI riref~arrylafe-r~efltarrol niisfirres.-Mixtures of methanol and methyl methacrylate of known composition and boiling-point were uniformly and slowly distilled in the Rosanoff apparatus at the rate of approximately I ml. per minute. Weighed fractions of the distillates were analysed by determinations of refractive indices and densities. The composition of each frac- tion was then plotted against the total weight distilled to the end of the fraction, and the composition of the first drop was found by extrapolation. This corresponded to the composition of vapour in equilibrium with the original mixture.

(b) Metlyl 111et11ac ylate-iiietliac ylic ncid iiiixtrrres.-Mixtures of methyl methacrylate and methacrylic acid were similarly distilled and weighed fractions of the distillate analysed by titrating the free acid content with O'IN. KOH using phenol- phthalein as indicator. The course of each distillation was also followed by refractive index and density determinations.

Liquid-vapour equilibrium curves and boiiing-point-liquid- vapour composition curves were plotted from these results. The curves showed the existence of a binary minimum boiling point minure of methyl methacrylate and methanol both at zoo inm. and 760 mm. Thus any fractionating column would have to be designed to give distillate of substantially the composition of this binary as light fraction. The curves also showed that the separation from methacrylic acid would be straightforward and simple. Tables I, 11, and 111 give the results obtained with the above mixtures.

TABLE I Boilitg poirrrs attd Roratrojfdisrillatiotts at 200 ittiti. of t tr~t l t jd itrerhacrylatc-

tircthairol ittisrrtras Composition of sample Methanol content of

distilled 1st dron of Methyl methacrylate distilhe

B. Pt. Wt. 1: Mots. '!A Wt. I!(, Mols. 100'0 100'0 0 99 ' 0 96.9 4'0 96 '0 94'0 10'0 96.0 88.5 19.5

30.0 91 ' 0 92.0 78.6

74'3 38.0 43'0

90.0 85 '0 80.0 75.0 . 49'0 70.0 42-75 54'5 60.0 32.4 57'0 50.0 24.3 62.5

67.6 40.0 30.0 12 '1 20.0 7'4 80.4 15.0 5 '4 83 '4 10'0 3'5 88 '3 5 ' 0 I -65 93'1

83'4 36.2

I 7 ' l 72.8

0 0 100'0

0 11.5 25 '7 43'1 57 '2 64 '0 65 7 70.2 74'2 77'2 78.9 80.5 83'9 86-7 88.3 92.8 94 ' 0 95'9 97'7

100'0