the heat of bromination

According to Hehner and Mitchell,1 “the action of bromine upon unsaturated bodies is instantaneous and is attended with a considerable evolution of ...
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y

Feb., 1916

the method as a n analytical procedure or working t h e process on a commercial scale may be had on application t o t h e author. COLLEGEOF THE CITY OF NEW YORK

B y J. W. MARDEN Received September 10, 1915 INTRODUCTORY AND HISTORICAL

According to Hehner and Mitchel1,l “the action of bromine upon unsaturated bodies is instantaneous and is attended with a considerable evolution of heat. It is complete a n d quantitative. * * * It is not complicated t o a n y extent by secondary reactions. T h e amount of hydrogen bromide formed measures the substitution, and is very small in most cases.” HehneP found this value, when a number of fats and oils were mixed with bromine, t o be as follows: FATOR OIL

Olive 1.5 t o 2 . 7

Per cent free H B r . .

must be determined, of course, with each individual apparatus, because of its heat capacity. Wileyl has proposed a more convenient method of TABLE 11-RESULTS

THE THERMAL VALUES OF THE FATS AND OILS I-THE HEAT OF BROMINATION

Castor 2.7

Boiled Butter Linseed 0.9 8.8

I21

WILSON (HEHNER-MITCHELL METHOD) IODINE NUMBER DEVIATION Rise in Experi- CacluOIL OR FAT temperature mental lated Absolute Per cent Cocoanut.. 1.4O C. 8.4 8.2 -0.2 -2.4 S. A. Tallow.. 7.3 44.0 43.2 -0.8 -1.8 Olive, pure.. . . . . . . . . . 14.0 82.0 82.5 0.5 0.6 Rape . . . . . . . . . . . . . . . . 1 8 . 0 103.4 104.5 -1.1 -1.06 BY

...........

........

handling t h e oil and bromine which he uses in somewhat t h e same way as Hehner a n d Mitchell. Table I1 gives a few of t h e results obtainedby Wilson,2 using the original Hehner a n d Mitchell method, which show very good agreement between t h e calculated value and t h e iodine number found by analysis. The work of Jenkins3 does not show such good concordance when a n a t t e m p t is made t o obtain t h e iodine number from t h e temperature rise by multiplication with a factor. TABLE111-RESULTS BY JENKINS IODINE NUMBER DEVIATION Exoeri- CalcuOIL mental lated Absolute Per cent ~Blown R a p e . . . . . . . . . . . . . . . . . . 5 5 . 3 54.1 18.8 34.0 Blown Cottonseed . . . . . . . . . . . . 78.1 62.2 15.9 25.6 72.4 71.6 Neat’s F o o t . . . . . . . . . . . . . . . . . . 0.8 1.1 80.1 Olive ........................ 1.4 1.7 81.5 - 0.36 84.1 Castor. ...................... 0.3 83.8 133.4 Japanese W o o d . . . . . . . . . . . . . . . 165.7 -19.5 -32.3 Raw Linseed. . . . . . . . . . . . . . . . . 174.3 - 0.04 - 0.02 173.9 ~

ore recently by McIlhiney’s m e t h ~ d however, ,~ t h a t there are a few fats and oils where t h e substitution is very large. Hehner and Mitchell also showed t h a t each oil, when treated with a n excess of bromine, gave a characteristic temperature rise and t h a t t h e quantitative d a t a obtained by this temperature change, when t h e fats and oils were mixed with bromine in a suitable tube, furnished more reliable d a t a on their purity t h a n t h e Maumen6 sulfuric acid test. They expressed t h e opinion t h a t a method worked out on this basis could well replace t h e longer method for t h e iodine number as a test for t h e purity of a fat or oil. I n their method I gram of oil, dissolved in I O cc. of chloroform, is placed in a Dewar vacuum test t u b e and exactly I cc. of bromine, previously brought to t h e same temperature as t h e oil solution, is added. The rise in temperature is measured by a n accurate thermometer graduated t o one-fifth of one degree. A test tube packed in cotton was first used b u t later replaced by a Dewar tube. As one would expect, t h e test tube packed in cotton gives lower results. The whole operation takes only a few minutes. Table I gives t h e results obtained b y Hehner a n d TABLEI-RESULTS OIL OR FAT Lard

HEHNER AND MITCHELL(a) IODINE NUMBER DEVIATION Rise in Experi- Calcutemperature mental lated Absolute Per ceht 10.6’ C. 57.15 58.3 1.15 2.0 - 2.1 37.07 36.3 --0.77 96.64 96.68 0.04 0.04 80.76 82.50 1.74 2.1 122.0 118.2 3.80 - 3 . 2 107.13 106.7 0.43 - 0 . 4 83.77 82.5 1.27 - 1.5 160.7 167.2 6.5 3.9 8 8 . 3 3 101.2 12.87 12.7 77.2 96.8 19.6 20.0 144.03 140.0 - 4 . 0 3 - 3 . 8 oyiltsch’s “Chemical Technology and es, Vol. I , Macmillan & Co. (1909). BY

.................

Olive. . . . . . . . Maize. ........... Cottonseed. . . . . . .

Cod Liver.

...

-

Mitchell. The rise in temperature due t o t h e bromination of each oil multiplied b y t h e factor 5.5 very nearly gives t h e same value for t h e iodine number as Hehner a n d Mitchell obtained experimentally. The factor 1 2

*

Hehner and Mitchell, Analyst. 1896, p. 148. Hehner, Analyst, 1896, pp. 20, 49. McIlhiney, J. A m . Chcm. Soc., 2 1 (1899). 1084.

-

Since there are many discrepancies between t h e two iodine values, i t is suggested4 t h a t each individual oil be given a constant t o suit t h e apparatus in which t h e work is done. This would, of course, make this method too cumbersome for practical use in replacing the method for t h e determination of the Hub1 iodine number. Gill and Hatch’ have tried the method with about t h e same degree of success. More recently SteipeP has published several contributions on t h e determination of t h e iodine number of t h e fats and oils by means of t h e bromine thermal test. He has repeated practically all of t h e previous work a n d his results agree well with former determinations. He finds t h a t he is unable t o calculate t h e iodine number from t h e bromine thermal value with accuracy but t h a t he must have a constant for each individual oil and each apparatus. An a t t e m p t has been made also t o throw some light on t h e structure of certain unsaturated compounds when they combine with bromine. Louguinene and Koblultoff’ have measured the heat produced when various compounds dissolved in carbon tetrachloride react with bromine, alsodissolved in carbon tetrachloride. They found t h a t t h e heat of solution of most fats and oils in carbon tetrachloride is very small a n d t h a t the heat produced per gram molecule of bromine, when accurately determined, varies considerably with each individual compound. I n spite of these tests, however, there has been no technical attempt t o measure the heat of bromination of t h e fats and oils by a rapid calorimetric method and t o p u t this de1

J A m . Chem. Soc., 18 (1896), 378.

a

Chem. News, 1896, p. 87.

8

J. SOC.Chem. Ind.,

16 (1897), 194.

‘ Archbutt, J. SOC.Chem. Ind., 189’7, p. 310. J . Am. Chem. SOC.,2 1 (1899), 27. OSteipel, Seifenfabrikant, 8 1 (1911), 349, 393, 421, 445, 473, 501, 525. Louguinene and Koblukoff, J . Chem. Phys.. 4 (1906), 209 and 489; 6 (1907), 186; Comfit. rend., 160 (1910). 915. 6

’

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY

I22

termination on t h e same scientific basis as many of our other calorimetric tests. OBJECT O F THIS P A P E R

The object of this paper is t o devise a n apparatus for t h e rapid calorimetric determination of the thermal reactions of the fats and oils, and to determine t h e heat of bromination of some of t h e m ; also t o show whether or not the iodine number calculated from t h e true heat of bromination compares favorably with experimentally determined iodine numbers. APPARATUS

The apparatus for these experiments consists in a n especially constructed mixing chamber placed in water contained either in t h e ordinary form of water calorimeter or, as it has been more recently used, in a large Dewar tube. il small calorimeter was also devised for t h e rapid although somewhat rough determination of t h e specific heats of t h e brominated oil mixtures. Figs. I , I1 and 111 show these pieces of apparatus set up ready for use. In Fig. I, A represents t h e cross section of a Dewar tube, 7 x 3 0 cm., inside measure, and B represents a Beckmann thermometer. Fig. I1 shows a cross section of t h e mixing chamber, (Fig. I, M ) of copper 3.2 x 6.8 cm. inside measure with a flange (Fig. 11, F ) around the inside 0.5 cm. wide and 3.j cm. from the top of t h e chamber. The chamber is fitted with a cover of t h e same material. On t h e outside of this mixing chamber, there are four flanges 0.5 cm. wide andfastened a t a slight angle so t h a t when i t is rotated these wings stir the surrounding mater. The joint between t h e cover and t h e chamber is carefully ground a n d t h e cover is held in place and water-tight b y three or four small screw clips made for the purpose. The mixing chamber is connected by thin-warled glass tubing t o a shaft and pulley so t h a t i t can be rotated. A narrower glass t u b e passes down through t h e outside t u b e ; a t the lower end of t h e smaller tube is a small paddle stirrer and at the upper end a pulley. The mixing chamber was covered with a thin layer of paraffin t o protect it from t h e action of t h e acid and bromine. Fig. I11 shows a smaller Dewar tube 3 x 20 cm., inside measurement, containing copper wire stirrers C a n d D ,a Beckmann thermometer and a thin-walled glass t u b e T 0.8 x 23 Em. sealed off a t t h e bottom. The use of these instruments will be described with the sample experiments given below. The Beckmann thermometer readings were corrected by a certificate (from t h e U.S. Bureau of Standards). The pipettes were all calibrated with water a t 2 0 ’ c. T H E OILS AP;D R E A G E N T S

The oils used for these experiments were mostly commercial samples, t h e origin as far as possible being stated in Table VI, The bromine used was Merck’s best, free from chlorine and iodine. Archbutt’ has found t h a t commercial samples of bromine give about the same temperature rise as more carefully dried samples so t h a t especial care was not taken t o d r y t h e bromine. A good grade of technical carbon tetrachloride was used. The mineral oil was Liquid Petrolatum, U. S. P. “snow-white” sold by J. S. 1

Archbutt, J . SOC.Chem Ind., 1897, p 310

VOI. 8 , KO. 2

hferrell Drug Co., St. Louis. The solution of bromine in carbon tetrachloride was made in t h e proportion of I t o 3, by weight, respectively, because a solution, of this strength can be handled conveniently in a burette if t h e upper end of t h e burette is connected t o a potassium hydroxide absorption apparatus. All other reagents used were carefully tested for their purity and the standard solutions were twice checked for their strength. STAKDARDIZATION O F T H E CALORIMETERS

The calorimeters were standardized by using t h e heat liberated by t h e dilution of suifuric acid of known concentration. Bronsted’ has very accurately determined t h e heat of dilution of sulfuric acid by the method of mixtures. using a n 8-liter calorimeter. Table I V gives the results obtained by Bronsted. When t h e d a t a in this table are plotted (the moles of water per one mole of acid against t h e calories of heat developed), a curve is obtained from which the heat of dilution can be read for any number of moles of water per mole of sulfuric acid. TABLE11’-HEATS

OF DILUTIONOF S G L F U R I C ACID (BROXSTED)

Moles Hz0 Calories per 1 mole HzSOa of heat 0.1 0.806 0.2 1.586 0.3 2.331 0.4 3.054 0.5 3.750 0.6 4.418 0.7 5.054 0.8 5,654 0.9 6.212 1.0 6.710

Moles H20 Calories per 1 mole HzSO. of heat 1.5 8.790 2.0 10.020 3.0 11.640 12.830 4.0 5.0 13.710 6.0 14.370 7.0 14.890 8.0 15.260 9.0 15,580

In standardizing t h e large calorimeter (Fig. I) sulfuric acid (the strength of which had been checked

%7 FIG.I

FIG.I1

FIG.I11

b y specific gravity and by precipitating and weighing t h e barium sulfate) was weighed out into t h e lower compartment of t h e mixing chamber; a “medium thin” coverglass, such as is used for microscopical work, was then sealed on t h e ledge with paraffin and a weighed amount of water placed in t h e upper compartment. The mixing chamber was next clamped together as shown in Fig. 11, t h e inside stirrer being 1

Z . p h y s . Chem., 68 (1909), 693.

T H E JOCTRNAL O F I N D U S T R I A L A N D ENGINEERING CHEMISTRY

Feb., 1916

held up by a small sized paper clip. The mixing chamber was then plunged into t h e water in t h e calorimeter, which had been previously weighed. When t h e apparatus was all in position (Fig. I ) , t h e mixing chamber was rotated a n d t h e water in the Dewar t u b e stirred by t h e flanges. When t h e temperature had been read on a calibrated Beckmann thermometer four or five times a t one minute intervals t h e small inside stirrer was loosened and forced down, breaking t h e coverglass a n d mixing t h e acid a n d water inside of t h e mixing chamber. The small stirrer was rotated in t h e opposite direction t o t h a t of t h e mixing chamber, t o insure rapid and thorough mixing of t h e acid a n d water. The temperature rise was nbted each minute a n d calculated in t h e same way t h a t t h e temperature rise is found a t present in t h e calorimetric determination of coal.’ The time of half t h e total temperature change was about I minute. It took approximately 4 t o 5 minutes t o reach t h e maximum temperature, when t h e stirrers made about 300 revolutions per minute, so t h a t t h e total rise in temperature was corrected for I minute a t t h e rate of change before breaking t h e coverglass a n d for 3 t o 4 minutes at t h e rate of change after. The specific heat of t h e diluted sulfuric acid in t h e mixing chamber, needed in the subsequent calculations, was taken from the work of Biron,2 his data being given in Table V. TABLE v-SPECIFIC Moles H20 per 1 mole %SO4 0.0 0.4856 1.0 2 3 4 5 6

HEATSO F DILUTEDSULFURIC ACID (BIROL) Specific Moles Hs0 Specific heat per 1 mole Hi304 heat 0.3352 7 0.6475 8 0.3786 0.6771 9 0.4408 0.7020 10 0.4628 0.7231 11 0.5012 0.7412 0,5420 12 0.7584 13 0.5805 0.7717 0.6152 14 0,7837

When these data are plotted, t h e specific heat against t h e moles of water per one mole of sulfuric acid, a curve is obtained from which can be read the specific heat of a n y concentration of sulfuric acid. A statement of t h e d a t a obtained in one of the determinations of t h e heat capacity of the large calorimeter a n d a subsequent calculation of this will best illustrate t h e use of t h e apparatus. READINGOF

THERMOMETER-OC.

STATEMENT OF DATA WEIGHTS Acid and Mixing Chamber. . . . . . . . . . . . . . . Mixing C h a m b e r . . . . . . . . . . . . . . . . . .

GRAWS 80.7455 46,1024

................... Paraffin and Glass..

..

Water ...........................

19.8314

O0

.....

METHOD

TemperaTime ture 1 1 . 31 1 ,795 11.32 1.803 11.33 1.813

11.41 4.470 11.42 4.470 11.43 4.470 1.823O C.

O F CALCULATIOK O F T H E H E A T CAPACITY OF THE

LARGE

CALORIMETER

By repeated trials t h e sulfuric acid was found t o 1

Noyes,

THIS JOURNAL, 5 (1913), 527.

2. anovg. Chem., 43 (1905), 48.

123

have a n average specific gravity of I . 7 7 j o j at 2 0 ’ C. which corresponds t o 84.61 per cent sulfuric acid by weight. One mole of acid, therefore, a t this concentration was mixed with o.gg012 mole of water. Accord-’ ing t o Bronsted’s curve the heat dilution a t this concentration is 6,650 calories. Each gram of t h e 84.61 per cent acid contains 0.008627 mole of sulfuric acid a n d 0.0085425 mole of water. The weight of acid used multiplied by 0.008627 gives t h e moles of acid used for a determination. Let this value equal X. The weight of t h e water placed in t h e upper part of t h e mixing chamber divided by 18.016 equals the moles of water weighed out. This value plus t h e product 0.0085425 multiplied by t h e weight of t h e acid weighed out in t h e lower part of t h e mixing chamber equals the total moles of water used, which value divided by X gives the moles of water per mole of HzS04. The heat of dilution for this concentration is located on Bronsted’s curve, 6,6 j o subtracted from it, and t h e result multiplied by X , which is t h e total heat added to t h e system. The result divided by t h e total corrected temperature rise gives the number of calories necessary t o raise t h e temperature of t h e system I O C . , which value must be corrected for t h e heat capacity of t h e diluted acid (Biron’s curve). The heat capacity of the coverglass and the paraffin was found t o be .so small and always so nearly t h e same t h a t it was unnecessary to take account of this factor. A sample calculation of t h e water equivalent of t h e large calorimeter is given below, using t h e d a t a given above. Moles of Sulfuric Acid used ...... 0.29885 Total Moles of Water used.

4.6735 moles water 6.790 calories in this case

H e a t of Dilution a t this concentratio Calories per 1

........ ..

0.57 31 .O

calories

Four determinations of the heat capacity of the larger apparatus were made: NO. 1 2 3 4 AVERAGE Value ..................... 739.0 739.8 736.1 738.5 738.3 T h e calculated value from the specific heats of the materials of the apparatus gave a value of 738.5 calories.

The above figures show a total variation of about 0 . 5 per cent. Undoubtedly, t h e average value is very close t o t h e t r u e one. Result No. 3 is much lower t h a n t h e other values, b u t no reason could be found for discarding it. The value 738.3 calories was taken as t h e heat capacity of t h e apparatus. T H E H E A T CAPACITY AND USE

O F T H E SMALL

CALORIMETER

The heat capacity of t h e small calorimeter (Fig. III), which was used for t h e specific heat determinations, was found in the same way as in t h e case of t h e larger calorimeter. Fifty grams of water were placed in t h e Dewar tube A’ and I cc. of sulfuric acid run into T from a carefully standardized pipette. Another I cc. pipette, filled with water and stoppered a t t h e top, was hung in T . The thermometer was placed in t h e water in A’ and when t h e temperature conditions were constant t h e stopper at the t o p of the pipette

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY

124

containing t h e water was opened and t h e acid and water in T allowed t o mix. By carefully standardizing t h e pipette and always allowing t h e same time for draining, very closely checking results were obtained. The stirring was done by hand with t h e copper wires C and D. I n determining the specific heat of t h e oils and their mixture, they were Placed in A’ in Place of the water, always using the Same volumes. The calculations were similar t o those for t h e other calorimeter and t o t h e ordinary specific heat calculations. T H E H E A T O F BROMINATION

Many oils like sandalwood and linseed oil, when added directly t o bromine, combine with i t with explosive violence, and much bromine is volatilized so t h a t the test can not be carried on quantitatively unless the reaction is made t o take place in a bomb calorimeter. I n order t o use t h e apparatus described it is necessary t o dilute the bromine or t h e oil in order to have a quantitative reaction. Wiley suggested t h e dilution of bromine with chloroform and others later have used carbon tetrachloride in place of t h e chloroform because there is practically no thermal change when bromine dissolves in it. I t was found advisable in t h e present work t o dilute TABLE VI-HEATS h.0. OILOR FAT 1 2 3 4 5 6 7

8

9 10 Castor (Highest Puri 11 Castor (Commercial) 12 13 14 15 16 17 18

OF

Vol. 8, No.

2

in t h e historical part of this paper t h a t t h e temperature rise obtained in the determination of the bromine thermal number multiplied by a factor does n o t in some instances check t h e iodine number. The heat of bromination is therefore compared with t h e Hub1 iodine number in Table VI. DISCUSSION O F R E S U L T S

The results in this paper were always checked under 0 . 5 per cent total variation, but it is not claimed t h a t they are closer t h a n 1.0 per cent of t h e true value since in certain cases, errors might be additive. I t is doubtful, however, if so much error could creep in with t h e experimental methods used. It will be seen t h a t about the same agreement is obtained when the heat of bromination is compared with the iodine number as when t h e temperature rise obtained by Hehner’s method is compared with the iodine number. I n all cases but two, the variation between t h e calculated a n d the observed iodine number is not great. I n these two cases t h e variation is considerable. A perfect agreement, however, should not be expected between these two values because when bromine reacts with t h e fats and oils not only direct additions take place such as happen in t h e determination of

BROMINATIOX (AUTHOR’SRESULTS) C O M P A R E D WITH I O D I N E NUMBERS

HSATO F IODINE NUMBER BROMINATION Found Calculated Author’s result S e xperimental factor 0.846 Unknown 274 270 232 Local Pharmacv 206 172.5 174.2 Local Pharmacy 169.0 173 204.6 156.0 127 Standard Varnish Works, Chicago 150.0 146.2 12.3. 1 123.8 E. H . Sargent Co., Chicago E. H. Sargent Co., Chicago 126.4 108.2 107 E. H. Sarrent Co., Chicago 120.8 105.8 102.2 99.0 117.0 101.7 Local Grocerv 9 3 . 4 92.2 109.0 88.1 88.8 104.1 86.5 87.5 102.2 86.5 83.2 102.2 8 4 . 0 85.2 Merck’s 100.7 80.0 81.7 96.6 Waldenburg & Scharr. Chicago 80.7 80.3 (California) Local Grocery 95.4 70.2 68.7 E. H. Sargent Co.. Chicago 83.0 67.2 68.6 Local M e a t Market 79.3 Nil ... Local Pharmacy SOURCE OF

OIL

t h e bromine with carbon tetrachloride and t h e oil t o be tested with a mineral oil which gave no thermal reaction with bromine, and t o mix t h e resulting solutions. I n one or t w o cases where t h e oil was very viscous or a solid fat was tried, they were diluted with carbon tetrachloride. I n t h e determination, t h e oil and mineral oil were weighed out into t h e lower compartment of t h e mixing chamber and a n excess of bromine dissolved in carbon tetrachloride (1:3 by weight), placed in t h e upper compartment. The apparatus was set up as described in t h e standardization and when t h e rate of temperature change was uniform the two solutions were mixed. The temperature rise was determined in the ordinary may. The calculation of the heat of bromination in terms of calories per gram of oil is simple. The heat capacity of the apparatus, 738.3 calories, plus t h e heat capacity of t h e bromine-oil mixture, multiplied by the total temperature rise a n d this value divided by t h e grams of oils used, gives t h e calories per gram of oil. The heats of bromination of a number of t h e common fats a n d oils are given in Table VI. It has been shown

...

DBVIATION Absolute -3 8 1.7 4.0 -29 0.7 1.2 3.6 2.7 - 1.2 0.7 - 1.0 3.3 1.2 1.7 0.4 1.5 1.4

-

-

Per cent -14.1 0.98 2.36 -18.6 0.57 - 1.12 - 3.4 - 2.6 - 1.28 0.79 1.14 3.96 1.43 2.12 0.5 2.2 2.04

-

-

t h e iodine number but also a varying amount of substitution occurs which in the case of many oils is small ( I t o 4 per cent), b u t in the case of others is quite large. Also, without knowing the way in which bromine may add, whether it adds t o doubly or triply-bonded carbon atoms, etc., one could hardly expect t h a t t h e heat, of bromine reactions would be comparable t o t h e weight of bromine or iodine absorbed. Louguinine and Koblukoff have shown too t h a t the molecular heat of addition of bromine to a molecule of oleic acid is 28,757 calories, to crotonic aldehyde 19,349 calories, and t o pinene about 36,000 calories. Such variation can not be due t o experimental error but the conclusion is t h a t if the iodine number and t h e bromine thermal reaction are exactly comparable it happens t h a t t h e bromine in many cases adds t o t h e oils in about t h e same way. I n certain instances, a t least, i t is evident t h a t this is not the case. CRITICISM O F T H E METHODS

I n a test such as has been proposed there are several factors t o be considered. An analysis on paper shows at least seven of these, although perhaps Nos. 3 a n d 5 in the list should be considered together.

Feb., 1916

T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY

I-The heat capacity of the apparatus. 2-The heat of separation of the bromine from the carbon tetrachloride solution. 3-The heat of solution of the brominated oil in the carbon tetrachloride. 4-The heat capacity of the brominated oil-carbon tetrachloride mixture. 5-The heat of solution of the mineral oil in the carbon tetrachloride. 6-The heat of bromination of the mineral oil. ./--The heat of bromination of the oil tested. If all of these values were large, determinations would be laborious but fortunately most of these factors are negligibly small. A discussion of these factors and a n elaboration of some good and bad points in t h e method, which have been brought out in this work, are given below. There is one case where the method in its present state can not be used. The heat of bromination of turpentine can not be determined with this apparatus because of t h e solubility of paraffin in this liquid. No great trouble was experienced due t o the dissolving of t h e paraffin except in this instance. Paraffin is very slightly soluble in carbon tetrachloride or carbon tetrachloride solutions of t h e oils. The use of a copper dish as a mixing chamber is not very objectionable unless the cover should leak, in which case, in t h e presence of a little water, bromine attacks t h e dish vigorously. The dish was cleaned after each experiment by dipping i t into hot paraffin which melts off t h e brominated oils a n d when t h e dish cools leaves a thin layer of paraffin over i t t o protect it in t h e next trial. It is suggested here t h a t a porcelain enameled dish would serve much better for this work and t h a t instead of a ground joint such as was used here between t h e cover and t h e mixing chamber, a small washer of thin gasket rubber be used t o make this joint tight. The heat of breaking the coverglass a n d t h e subsequent dropping through of t h e carbon tetrachloride solution of bromine was found to be nil. I n testing this, t h e bromine solution was p u t in above t h e coverglass in the mixing chamber and t h e lower compartment of t h e mixing chamber left empty. When t h e temperature conditions were constant t h e coverglass was broken in t h e usual way and t h e result noted. The heat of reaction of t h e bromine when i t goes out of carbon tetrachloride solution t o combine with t h e oils was found t o be very small. This heat has of course t h e same value with t h e opposite sign as the heat of solution of t h e same amount of bromine in t h e same amount of carbon tetrachloride. I n this case t h e bromine was sealed below t h e coverglass of t h e mixing chamber and t h e carbon tetrachloride above it. It was found t h a t every gram of bromine dissolving in three times its weight of carbon tetrachloride gave a lowering of temperature of about o.002' C. (heat capacity of apparatus, 738 calories). The heat of solution of the oils in carbon tetrachloride was also found t o be very small. Ten grams of mineral oil dissolving in 1 5 cc. of carbon tetrachloride give a temperature lowering of -0.015' C. The heat of decomposition of t h e bromine solution being "plus,"

125

t h e conditions were so regulated t h a t when I O cc. of mineral oil were used as a diluent and about 15 cc. of bromine-carbon tetrachloride solution were used were cancelled. for t h e bromination, these The heat of solution of most of t h e oils which were tried in carbon tetrachloride was very small. Castor Oil gave a lowering - o . 0 2 0 0 *' to -0.0300 C. per I O grams of oil in 15 cc. of carbon tetrachloride. If this oil is diluted with carbon tetrachloride, however, instead of mineral oil, this variation drops out. The specific heat of t h e brominated oil mixture does not vary greatly when about the same proportion of t h e oil t o be tested, mineral oil and the bromine solution, are used. The specific heats of some of t h e mixtures determined are given in Table VII. TABLEVII-SPECIFIC

HEATS

OF

MIXTURES

MIXTURE

SPECIFIC HEAT

These are cases, of course, where t h e ratios of oil, mineral oil, bromine and carbon tetrachloride are not much varied. This shows, however. t h a t under ordinary working conditions t h e specific heat need not be determined for every mixture b u t an average value can be taken. An error of several per cent in t h i s value is easily allowable. If there is, for instance, 50 grams of this mixture used in a determination a n d t h e specific heat is taken as 0.30 and t h e true heat capacity is 0 . 2 5 , in a n apparatus having a total heat capacity of 7 j o calories per O C. this would make a n error of 2 . 5 calories or less t h a n 0.4 per cent error. This specific heat value can also be closely calculated by t a k i n g ' t h e s u m of t h e heat capacities of the substances present multiplied by t h e weights of t h e materials used. For example, Table VI11 will show t h e calculated specific heat of t h e mixture containing China wood oil. TABLE VIII-CALCULATEDSPECIFIC HEATOF CHINAWOODOIL MIXTURE WT. USED SPECIFIC MATERIAL Grams HEAT Bromine.. . . . . . . . . . . . 9.07 0.107 Carbon Tetrachloride.. . 2 7 . 2 0.207 China Wood Oil. . . . . . . . 9.0 0.23 1 Mineral Oil , . . . . .. . . . . . 10.5 0.416

.

TOTALWEIGHT.. ...... SPECIFIC HEATOF

55.77

CALCULATED HEAT , CAPACITY 0.97 5.63 2.08 4.38

-

TOTALHEATCAPACITY,. . 13.06

13.06 MIXTURE= -- = 0.234 55.77

The specific heat figured this way is 0.234. It was found by direct determination t o be 0.254. These values check so closely t h a t t h e error is negligibly small. It is therefore unnecessary t o determine t h e specific heat of every mixture and if t h e method were t o be used much, a table could easily be prepared from which t h e specific heat of any proportioned ccmbination could be read with sufficient accuracy. The handling of 1:3 solution of bromine in carbon tetrachloride is easy in a burette, t h e upper end of which is connected t o a small wash bottle containing sodium or potassium hydroxide. If this is kept under t h e hood no discomfort is experienced on account of bromine fumes. Special attention should be called t o t h e specific heat apparatus. If a very quick method is desired

126

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

for t h e true heat of bromination, t h e apparatus could be worked in t h e same way as it was standardized, using oil and bromine in place of sulfuric acid a n d water. This should give results which are accurate t o perhaps I or 2 per cent. This should make also a convenient apparatus for certain student calorimetric work where i t could wcll be used in place of larger and more expensive types of calorimeters. I t might be noted, too, t h a t the stirring must be vigorous in the large calorimeter. Several types of stirrers were tried inside of t h e mixing chamber and a spiral form was finally adopted as being t h e most efficient for this purpose. CONCLUSIONS

I-A special apparatus and a method for the determination of t h e true heat of bromination have been proposed a n d tried. 11-A new apparatus on t h e same principle has been proposed for t h e quick determination of specific heat b u t i t could well he used for othcr purposes, such as t h e determination of heat of neutralization, the Rlaumen6 number in terms of calories per gram of oil, etc. 111-The heats of bromination in calories per gram of oil have been determined on a number of oils a n d these values compared with t h e iodine numbers. IV-It has been shown t h a t the heat of bromination is not directly comparable t o t h e iodine number, a n d t h e reason why such a n agreement could not be expected has been pointed out. V-The heats of solution of bromine and most oils in carbon tetrachloride have been shown t o be very small.

1'01. 8.

No. z

characteristic of this oil, and upon which is dependent t h e development of such varnishes as contain it. T h e report of t h e committee, submitted as a result of a series of tests carried out b y different operators upon accurately prepared samples, shows t h a t t h e method must be carefully handled t o produce closely agreeing results, and t h a t under ordinary circumstances it should not he relied upon t o detect adulteration under 5 per cent. T h e iodine jelly test, as investigated b y t h e same committee, seems b u t little better. However, as mentioned in a n earlier paper,' the gelatination of wood oil b y iodine in chloroform solution is subject t o a marked retardation b y t h e presence of small amounts of alcohol. This fact may explain some of t h e variations in results, as the different operators were not using chloroform from t h e same source, and n o doubt some of t h e chloroform might have contained traces of alcohol. T h e index of refraction of wood oil, ns has been pointed out b y various investigators, is considerably higher t h a n t h a t of other drying and semi-drying oils. All attempts t o calibrate, for analytical use, the variations in refractive index, due t o mixing other oils with wood oil, h a w been unsuccessful in establishing the use of the rcfrnctomctcr in the quantitative estimation of adulteration. I n this method

U N I Y B R S ~OP Y MISSOURI. COLUMBIA.M I S S O U ~

OPTICAL DISPERSION OF CHINESE WOOD OIL AS AN INDEX OF PURITY By E. E. \YARE

R ~ c e i v ~Novernher d 26. 1915

The peculiar properties exhibited by Chinese wood oil have led t o t h e development of some interesting methods of examination for t h e detection of adulteration. I n practically all cases, although t h e property upon which the individual method is based is characteristic enough t o warrant its use as the basis of a method of examination, difficulties have arisen in t h e control of t h e conditions of operation, in consequence of which different laboratories report widely varying results. The two methods offered b y Ware a n d Schumann,' one of which depends upon t h e insolubility of the sodium soap of elaeomargaric acid in absolute alcohol, a n d t h e other upon t h e insolubility of t h e light-converted elaeostearic acid glyceride in high gravity petroleum ether, produce accurate results when operated under properly controlled conditions of temperat u r e a n d concentration; b u t they do not seem adapted t o t h e use of t h e factory control laboratory. T h e heat test as modified b y Committee D-I, SubCommittee 111, of t h e American Society for Testing Materials,z is a logical method of analysis, inasmuch as i t depends for its accuracy upon t h e careful observation of t h e progress of a gelatination which is 1 f

Tmrs J o u a n ~6~ (1914). . 806. Pioc. An. SOC.T a l . Mal.. 1916, P. 204.

t h e temperature corwclioii i:,r:rlr is !:irxc rnough to make possible a n error of onL, plir IYWL ;or cvery degree variation in tcrnpcrn:orc cnxtroi. Thcrc csists also t h e difficulty of mnkin: n n c s n t t scttinx of t h e cross hairs of the rending telescope upcn t h e dividing line b'etween t h e illuminatcd and t h e dark fields. This difficulty is quite pronounced when using white light as a source of illumination, for t h e line of division between t h e fields is n o t sharp, even after a careful adjustment of t h e compensator, t o correct for dispersion. E. C. Holton2 noticed, when working with t h e Abbe direct reading refractometer, t h a t t h e rotation of t h e prism required for correct compensation for wood oil a n d for other oils is very different. He has gathered together considerable unpublished d a t a in a n a t t e m p t to calibrate this difference in compensator reading t o a point where he can make use of i t as a n analytical method. BrierS takes advantage of this property of abnor~ T H ~ ~ J O U F (1915).571. CNIL.~ 2

1

Private eornrnunieefion. Tam JOURNAL, 7 (1915). 953.