December, 1929
IYDUSTRIAL AND EAYGINEERISG CHEMISTRY
of the sodium bicarbonate treated specimens, however, caused the return of the normal color. Cherries leached with running hot water to remove sulfur dioxide were found to be considerably higher in pH value than those boiled repeatedly in water when both had reached less than 25 p, p. m. of sulfur dioxide, the pH values being 4.5 and 3.0. Other things being equal, Erythrosine should penetrate cherries leached with running hot water more rapidly than it does cherries boiled repeatedly in water. Additional experiments proved the efficacy of the sodium bicarbonate solution of the Erythrosine for dyeing the cherries and the desirability of acidifying the sirup after dyeing in order to fix the color. Comparison of various concentrations of Erythr osineshowed that a 0.1 per cent solution gave as good results as more concentrated solutions. Applying the results of these experiments to the practical
1269
preparation of maraschino style cherries showed that rapid dyeing of the cherries is accomplished by adding Erythrosine in dilute (0.3-0.1 per cent) sodium bicarbonate solution and that practically complete fixation of the color is then obtained by adding a dilute citric acid solution (approximately 0.5 per cent). Summary
The pH value of the cherries and that of the solutions used in the dyeing of cherries with Erythrosine greatly affect the evenness and rapidity of dyeing and the fixation or the bleeding of the color in dyed cherries. Ponceau 3R and Amaranth are not appreciably affected by the pH value and bleed rapidly a t all the pH values used in the experiments here reported. It is recommended that Erythrosine be applied in dilute sodium bicarbonate solution of approximately pH 7.5 and be fixed by dilute citric acid or other permissible fruit acid a t approximately pH 3.0-3.5.
Vapor Pressures and Other Physical Constants of Methylamine and Methylamine Solutions' W. A. Felsing and A. R. Thomas UNIVERSITY O F TEXAS, AUSTIN, TEXAS
The vapor pressures of methylamine have been deH E introduction of reheats of evaporation of liquid termined from - 8 0 " to -10" C. and combined with frigerating units i n t o m e t h y l a m i n e f r o m vapor the data of Berthoud to obtain a general relation from home refrigerators has pressure data, are included. -90' to 156.90"C. (critical point). been exceedingly rapid in reThe use of methylamine as The densities of liquid methylamine have been dea refrigerant does not seem to cent years. Most of t h e s e termined from -80" to 20' C. units use as the refrigerating be accompanied by great danThe total pressures of methylamine solutions have ger in case of leakage, etc. fluid some of the more easily been measured for concentrations 1.67, 7.64, 13.39, Frankel (7) d i s c u s s e s t h e condensable gases, such as 22.86, 36.12, and 48.60 mol per cent. The partial presphysiological effect. Monosulfur dioxide, butane, methyl sures have been measured for a number of dilute soluchloride and ammonia. A m e t h y l a m i n e irritates the tions. comprehensive list of possible mucous membranes, and its The total heats of solution have been measured; the fluids for refrigerating units is odor is similar t o that of study of the change of this heat with the concentration ammonia. T h e c r a m p i n g given by Taylor (19). The of solution formed will be studied in detail. two systems in common use effect of ammonia is lessened The heats of evaporation have been calculated. by the substitution of methylare the compression and the groups for hydrogen. Metha b s o r u t i o n t v u e s . Both types utilize as the cooling principle the heat absorption when ylamine causes a slight depression of the blood pressure, but the liquid fluid evaporates. The two types differ, however, it does not alter the rate of breathing. The hematolytic in the method of causing rapid evaporation and in the method action of methylamine is due to the hydroxyl ions produced. of again liquefying the gaseous fluid. In the compression units Frankel concludes with the statement that methylamine is the fluid is liquefied by mechanical compression iind cooling much less poisonous than ammonia. The irritating odor of (generally air-cooling); in the absorption units the gaseous methylamine would seemingly call attention to a leak before fluid is absorbed by a solid or liquid absorbent during the any serious physiological action could take place. cooling portion of the cycle, and is then boiled out or driven Existing Data out by heating the solution or absorbent. The various types of apparatus employing the absorption principle a1e discussed Berthoud (1) measured the vapor pressures of methylby Keyes ( I S ) . amine from -7.55' t o Sl56.9' C. (critical point). The The fluid usually employed in the absorption units is International Critical Tables cite Berthoud's data a t even ammonia. With certain materials of construction and some temperatures, using smoothed-out values. The probable absorbents, however, this fluid has some disadvantages. accuracy of the data is stated t o be 5 in the last figure given, Monomethylamine, CH3.NH9, has often been suggested as a the pressures being listed in atmospheres; this means an possible substitute for ammonia in such cases. Since rela- accuracy for the first nine determinations to within 38 mm., tively few data on the physical properties of this substance and for the others to within 380 mm. Several authors (8, exist in the literature, it was thought profitable to determine 1 2 , 16) give values for the boiling point under different barothe vapor pressures and densities of liquid nitthylamine metric pressures. The International Critical Tables cite a and the total and partial pressures of methylamine solutions value identical with that of Olsen. a t different concentrations and temperatures. A few preVery few density values are available. Hoffman ( l a ) , liminary measurements of the heat of solution of methyl- Hodgeman and Lange (11), and the International Critical amine vapor in water, together with the calculation of the Tables cite values a t differing temperatures. Received August 7, 1929 The data on the partial pressures of methylamine out
T
\
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1270
of methylamine solutions are limited to a few data by Doyer ( 5 ). The heat of solution and the heat of dilution have been determined, incidentally, by Bonnefoi ( 2 ) . Methods and Apparatus
VAPORPREssuREs-since Berthoud's data ( 1 ) only included measurements from 1 atmosphere up to the critical pressure, it was decided to investigate the temperature range from the freezing point to the normal boiling point. The method was a static one similar to that employed by Felsing and Durban (6) in their work on acetone. Thermometer. A platinum resistance thermometer of the flat-coil, silver-sheath type was used in connection with a Mueller bridge of Leeds & Northrup manufacture. The thermometer had been calibrated a t 0" and a t 100" C. by the U. S. Bureau of Standards, and was calibrated during this investigation by the method of Keyes, Townshend, and Young (15) a t the freezing point of water, the freezing point of mercury, the sublimation of carbon dioxide, and the boiling point of oxygen. The vapor pressure functions employed for
fluctuations of the cryostat were not large enoush to cause pressure variations, over a period of 10 to 15 minutes, greater than 0.1 t o 0.4 mm. The average of eight to ten determinations at any given temperature is therefore considered to be accurate to 0.3 mm. DEXSITIES-AU density determinations were made with a pycnometer of the closed type, described by Felsing and Durban (6). The pycnometer was constructed of Pyrex glass (G-702-EJ). The volume a t each scale was determined by filling with pure, dry mercury under a high vacuum, cooling t o 0" C. in a thermostat, reading the mercury level in the capillary, warming to room temperature, and weighing. The weights used had been calibrated by the U. S. Bureau of Standards; all weighings were corrected to a vacuum. The volume of the capillary .per millimeter of length was determined by several trials, after testing the entire length for uniformity of bore. The volumes of the pycnometer itself a t any temperature and scale reading were calculated from the determined volume a t 0' C. by means of relation V T Pyrex = Vo [0.998325 2 316 X lo-'. T
+
2763
HEATER t
\
carbon dioxide and for oxygen were those of Cath ( 4 ) and Henning (9), respectively. A functional relation between temperature and the resistance in ohms was obtained, which was employed in calculating all temperatures of the vapor pressure and the density determinations. Cryostat. The cryostat was essentially of the type described by Walters and Loomis (23), the modifications being those devised by Felsing and Durban (6). Manometer. The manometer was of the type employed and described by Taylor and Smith (20). The manometer readings were made with a calibrated cathetometer and were considered accurate to 0.05 mm. The temperature
Vol. 21, s o . 12
x
+
i o - 8 . ~ 2
- 2.2 x
10-11.~31 (1)
This relation was based upon the determinations of the linear coefficient of expansion of Pyrex glass (G-702-EJ) over the temperature range 180" to 280" K. by Buffington and Latimer ( 3 ) . It was considered more accurate for the temperature range covered by this investigation than the equation proposed by Keyes, Taylor, and Smith (14). I n this relation 1'0 is the determined volume a t 0" C. Loading Apparatus. The methylamine was introduced into the piezometer or into the pycnometer according t o the scheme of Felsing and Durban (6) for acetone. The generator was an all-glass apparatus, connected through a drying train of small pebble-size sodium hydroxide particles, sods lime, and metallic sodium in mire form. The sodium wire reservoir mas surrounded, in turn, by liquid air, liquid ammonia, and ice. This reservoir was connected to a storage reservoir, from which the methylamine was drawn, by distillation, as needed. TOTAL A S D PL4RTIAL PRESSURES O F hfETHYLAMISE SOLUnoh-s-The scheme of measuring the total prewures of methylamine solutions a t different concentrations of methylamine and a t different temperatures was, in the main, that of Wilson (24) in his work on ammonia. A sketch of the apparatus is given in the accompanying illustration; it was an all-Pyrex apparatus. The manometers were of the simple and compound type. After all measurements had been made on a given concentration-i, e., a t different temperaturessome of the solution in the piezometer was drawn off to flush the capillary withdrawal tube; a sample was then taken for analysis by collecting it in a weighed quantity of standard sulfuric acid. The excess acid was determined by weight titration with standard sodium hydroxide, using methyl red as indicator. This determination of methylamine concentration was considered to hold, even though the solution was subjected to different temperatures during the total pressure measurements. The volume of the gaseous phase was quite small compared with that of the solution, and the vapor phase was always greatly overheated by the surrounding heating coil. Calculations showed the changes in concentration of the solution to be negligible. The partial pressures cover only a limited range. They were made by Schneider ( I ? ) by a six-bulb series air-bubbling method. The concentration of the solution was the same in all six bulbs, but only the concentration of the last bulb was determined before and after a run. Usually only a very small change in concentration was observable. The methylamine and water leaving the last bulb were absorbed
December, 1929
INDUSTRIAL AXD ENGI,VEERISG CHEJfISTRY
in standard 0.5 S sulfuric acid in a weighed absxption bull). Any moisture leaving this bulb was absorbed by a separate tared bulb containing concentrated sulfuric acid. The dry air was introduced into the train at about 1.25 liters per hour, the total volume of air varied from 2 to 18 liters, depending upon the concentration and temperature. All the usual precautions of accurate analytical procedure were observed, and all titrations were made with weight burets. TOTAL HEATOF SoLuTrox-The determinations of the total heats of solution of gaseous methylamine were made by Rillis IT.Floyd, of this laboratory. The complete investigation will appear in a later paper, but these preliminary values are given here to make this study more complete. The determinations mere carried out in a calorinieter essentially the same as the one employed by Stiles and Felsing (18) except the calorimeter itself was kept in a thermostat at 25" C., and the same precautions were observed. PREPARATION OF PURE?\IETHYLAMISE-The best c. P. methylamine hydrochloride was recrystallized from absolute ethyl alcohol, from n-butyl alcohol, and from triple-distilled water (concentrating under reduced pressure). The methylamine was generated from the solid hydrochloride, after evacuation to remove air from the generating and drying system, by the treatment with a concentrated sodium hydroxide solution. The gaseous methylamine passed 01-er solid sodium hydroxide and soda lime into a reservoir filled with metallic sodium in wire form and surrounded by liquid air. After a considerable quantity had been collected, the flask was warmed with liquid ammonia and finally with crushed ice. At this temperature the sodium removed the moisture, as evidenced by a slight hydrogen evolution. The reservoir and contents n-ere again frozen by a liquid air bath. the system highly evacuated, and the methylamine distilled into another reservoir containing metallic sodium. The Same operations followed. The dry methylamine was finally collected in a reservoir surrounded 11s liquid air, whence it was sent into the piezometer or pycnometer by distillation under very lorn pressures. I n making solutions of methylamine all precautions except that of drying were followed. The most concentrated solutions were niade by absorbing the methylamine in mater cooled by an ice-salt mixture. I n the heat-of-solution determinations the methylamine gas n-as dried by a long train of solid sodium hydroxide, soda lime, and metallic sodium wire. No effort was made to eliminate traces of hydrogen gas. Experimental Data
VAPORPRESSURES-DeterminatiOnS were made over a range of -80" to -10' C. The first eleven values of Table I are the data of this investigation; the others are due to Berthoud ( I ) , Hoffman (12),Gibbs ( 8 ) )and Olsen (16). Several readings Tvere made for each temperature. The observed data were plotted, on large scale, as loglo p (mni.) against 1/T. The data of Berthoud were used to extend the range to the critical temperature, even though ihey were apparently not made n-ith the same accuracy. The combined data may be expressed by the relation
+
log,, p(mm.) = - 138 60647/T 38.730167 loglo T - 6 600156 X lo-* T 3.870056 >< T Z - 757030015
volume of the pycnometer was made by means of Equation 1. The correction for the amount of methylamine remaining in the vapor state in the volume above the liquid level in the sealed off pycnometer was applied with the aid of the vapor pressure relation ( 2 ) and the gas law. The densities are recorded in Tables I11 and IT'; the observed values mere plotted on a large graph and a curve drawn. The relation between density and temperature is given by = 0.93249 - 6.09221 X 10-4. T - 106.443 X T* (3)
D (density, in grams per cc.)
This relation reproduces the observed values with a mean deviation of 1 part in 5400; the relation is believed to give true values of the density to 1 part in 6000. Table I-Vapor Pressures of Methylamine VAPOR PR~SSWRES VAPOR PRESSURES Calcd. Calcd. S o . TEMP. Obsd. by (13) KO.TEMP. Obsd. by (13) C. Mm. Mm. c. 1 -80.00 6.40 15 -6.0 6.42 768.3 787.7 2 -74.97 10.03 10.03 15.4 1976.0 1900, n 16 3 -65.83 21.35 21.48 17 4 1 . 0 4506.8 4520 3 64.29 64.29 18 5 1 . 4 6057.2 6134.8 ? -50.94 - 4 2 99 i n 8 97 108.51 8816.0 65.2 8880.9 19 6 7 5 . 5 11506 154.72 20 11465 7 9 4 . 1 17708 218.11 21 17436 8 403.34 22 112.4 25323 25272 9 465.61 32316 2 3 1 2 5 . 5 32376 10 24 136.1 39170 39052 5S6.39 11 655.51 25 1 4 4 . 5 45106 45144 12 734.1 26 1 5 0 . 5 49947 49955 763.1 27 1 5 3 . 5 52592 52514 13 - 6 70 755 8 ( 8 ) 14 - 6 . 6 0 760 0 (16) 767. 1 86549 28 156.9 55936 Table 11-Vapor Pressures a t Even Temperatures ?io TEMP. VAPORPRESSURES No. TEMP. VAPORPRESSURES c. Mm. ‘limos. C. Mm. Afmos. 1 40 4383.8 5 768 - 90 2.45 15 2 7.757 6.42 16 80 50 5895,6 15.33 17 60 7762.6 10.214 70 3 70 13.191 4 10030 33.64 18 60 16.771 12746 5 50 80 68.55 19 21,001 13961 90 20 6 -40 130.80 25.989 19752 100 21 7 235.39 30 22 31.735 24119 110. 402.07 -20 8 38.418 29198 9 120 23 655.51 10 46.127 35054 130 24 760.00 10 - 6 79 1,000 54.991 41793 140 11 - 0 1.349 25 1025.08 65.180 49537 2.032 1544.4 12 10 150 26 73,091 27 2.961 2250.5 20 1 5 6 . 9 55549 13 4.186 14 3181.6 30
--
(2)
where 11 is expressed in millimeters and T in degrec.s Kelvin. This relation reproduces quite accurately the data of this investigation, but does not reproduce Berthoud's data with any such accuracy. I n fact, any smooth curve through his data does not reproduce the observations better than does this relation. DESSITIES-h accurate calculation of the change in
Table 111-Obser ved and Calculated Densities CALCD.B Y (7) TEMPERATURE OBSD. Gramicc. Gram/cc. O c. 0.77774 -82.58 0.77787 0.76915 -74.19 0.76903 0.75878 -64.25 0.75S50 0.74949 -55.52 0.74931 0,73734 0.73719 -44.31 0.72857 0.72884 0.71124 -36.37 0.71114 -20.94 0.70267 0.70273 0,6992 (16) -13.60 0.69924 -11.00 0.69941 -10.80 0.699 f f 1 ,12,) 0 69413 0.69423 - 6.30 0.68446 0.68447 1.86 0.67346 0,67335 10.99 3.66586 0.66575 17.21 0,66270 1 9 ,78 0.66277
so
1 2 3 4 5 6 7 8 9 10
11
12 13 14 15
Table IV-Calculated TEMP.
hTO.
1
2 3
; 2
+
1271
b
9 10 11 12 13 14 15
c.
- 90 -so -70
- 50 -00 - 40 - 30 - 20 - 10 - 6.79 0 10 20 30 40
Densities and Specific Volumes DENSITY B Y (7) SPECIFIC V O L U M E Gram/cc. Cc./pi am 1.27354 1.29012 1 ,30753 1,32576 1.34489 1 35501 1,38613 1,40837 1,43170 1,43735 1.45630 1,48227 1.50959 1.53848 1,56902
TOTALPRESSURES O F l\IETHYL.4MIXE SoLrrTIoss-The total pressures (methylamine and m t e r vapor) are given in Table T'.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1272
PARTIAL PRESSURES O F ?LlETHYLBLfINE SoLunoss-The partial pressures of the methylamine solutions a t a given concentration and temperature are obt>ainedby the relation
p (methylamine)
P X m M
=-
(4)
where m is the number of mols of methylamine evaporated into the air passed over, P is the total pressure in the last bulb of the system-i. e., the average barometer reading plus the average manometer reading-and M is the total number of mols of air, water, and methylamine leaving the last (sixth) bulb of the saturating system. The observed data are presented in Table VI. Table V-Total Pressures of Methylamine Solutions PRESSURE TEXP. PRESSURE TEMP. PRESSURE
TEMP.
CONCN. 1.67 MOL PER CENT 0
c. -.
n.8 20.0 35.0 45.0 55.0 66.8 84.0
Mm. 7.0 22.9 54.8 91.7 149.3 251,2 512.9
c.
25.23 30.17 40.44 49.90 60.33 69.97 79,97 90.09
Mm. 56.8 74.1 128. 9 206.2 333.2 501,s 749.4 1095.2
CONCN. 36.15 MOL PER CENT
CONCN. 22.86 MOL P E R CENT
1.43 20.84 29.95 40.00 49.91 60.00 69.07 75.40
COXCN. 7.64 MOL PER CENT
73.2 242.4
300.8
466.1 694.8 1022.5 1446.5 1738.0
-0.45 t-9.93 19.80 29.87 39,87 49.91 59.98 71.92
190.6 309.1 473.4 708.9 102s.s 1453.2 1724.0 2951.0
CONCN. 13.39 MOL P E R CENT 0
c.
20.83 29.89 39.88 49,92 59.96 69,97 79.98 89.91
Mm. 62.1 130.3 216.7 342.0 526,O 780,2 1135.3 1607.4
COXCN. 48.60 MOL PER CENT
10.7 18.65 26.99 40.68 49 04 52.60 58.56 67.59 73.54
734.3 773.0 1182.3 1852 2419 2703 3220 4078 4871
Pressures of Methylamine from Solutions PARTIAL PARTIAL CONCN. PRESSURE CONCN. PRESSURE No. MOLAL TEMP. CHs-NHz No. MOLAL TEMP. C H I - N H Gram mob/ C. Mm. Gram mols/ O C . Mm. IO00 grams H10 1000 grams Hg0 0.8 0.81 14 1 0,5101 1,0464 45.0 22.15 1.28 0.8 15 1.2647 45.0 26.50 0.7955 2 1.79 0.6‘ 0.1873 6.12 1.1241 16 .55. 0 3 2.79 20.0 17.85 0,5147 4 17 55.0 0.5373 4.42 20.0 1s 0,8548 5 5 . 0 28.48 0,7989 5 20.0 19 1,0223 34.18 6.18 55.0 1.1177 6 35.0 1.66 55.0 20 0.1368 1.2264 42,30 7 33.0 7.41 21 0.5839 0.1302 10.01 8 75.0 35.0 22 10.33 0.8126 0.2421 18.83 9 75.0 35.0 23 13.70 1.0646 0,5300 75.0 10 41.72 24 3.67 45.0 0.1813 0,8403 75.0 11 66.30 12 45.0 0.5199 1.2632 75.0 25 10.96 100.00 17.42 45.0 0.8314 13
Table VII-Total No.
Heats of Solutions of Methylamine Vapor N 8
Calculated Heats of Vaporization of Methylamine
The heats of vaporization, over a limited range, were calculated by means of the Clapeyron relation AH, = T ( u ~ vn)dp/dT
(5)
where v1 is the molal volume of the vapor and u2 the molal volume of the liquid. The values of d p / d T were obtained
s o . 12
from the differentiated form of the vapor-pressure relation ( 2 ) , after it had been multiplied by 2.3026; the relation used was d p / dT - 319.1532 I 38.730167 15,19752 (mm./deg.) T2 T
[
lo-*
+ 17.82234 x
10-5Tl.p
(6)
The values of o1 were calculated from the perfect gas law; the deviations, for the temperature-pressure range covered, are quite small, as judged by the calculations made with the van der Waals equation. The constants a and b of van der Waals’ equation for methylamine were calculated from critical data given by Vincent and Chappius ( 2 2 ) and by Berthoud (1). The values of u2 were calculated from the density relation given in Equation 3. The calculated values of these heats of vaporization are given in Table VIII. Table VI11-Calculated Heats of Vaporization of Methylamine TEMP. VAPORPRESSURE d p / d T No. AH, = c. Mm. 1 218.4 70 1R.32 1.266 2 2.514 60 33.63 217.5 3 50 68.55 4.650 216.4 4 -40 130.80 8.053 214.4 5 30 235.39 13,193 212.3 20 403.07 20 554 209.8 6 7 - 10 655 51 30.623 207.2 8 6.79 760 00 34.507 206.4 6 0 1025.1 43 861 204.5 9 201.6 10 10 1.544 4 60 626 11 198.7 20 2250 5 73.114 12 30 3181.6 105,563 195.3
--
-
Thompson (21) presents an interesting relation for calculating the heat of vaporization a t the boiling point:
Table VI-Partial
TOTAL HEATSOF SOLUTION OF METHYLAMINE VAPORThese data (Table VII) are preliminary data and are subject to a more complete verification. They are included in this paper for the sake of completeness and to point out the discrepancy in these data and the two determinations of Bonnefoi (8). N is the ratio of mols of water to mols of methylamine dissolved (as determined by analysis), and Q is the heat evolved per gram mol of methylamine dissolved to produce the solution whose mol ratio is A-; the temperature is either 25” or 30” C.
Vol. 21,
P log10 P = 10.31(D~)‘/a
(7)
where P = DL/D,-i. e., the ratio of the density of the liquid to the density of the vapor a t that temperature. He claims considerable accuracy for this relation. For methylamine a t its normal boiling point the value becomes 207.4 calories per gram, a value to be compared with 206.4 calories per gram in Table VIII. The molal-entropy increase attending vaporization a t -49.6’ C. (the temperature a t which the vapor concentration is 0.00507 mol per liter) has been calculated to be 30.4 calories per degree. This value places liquid methylamine, according to Hildebrand (IO), into the class of polar liquids. Literature Cited Berthoud, J. chim. phys., 14, 14 (1917). Bonnefoi, A n n . chim. phys., [7] 2S, 362 (1901). Buffington and Latimer, J . A m . Chem. SOC.,48, 2305 (1926). Cath, Leiden Comm., 152d (1918). Doyer, Z . physik. Chem., 6, 486 (1890). Felsing and Durban, J . A m . Chem Soc., 48, 2885 (1926). Frankel, “Arzeneimittelsynthese,” pp. 68, 76-78, Julius Springer, Berlin, 1927. (8) Gibbs, J . A m . Chem. Soc., 27, 859 (1905). (9) Henning, A n n . Physik, 45, 287 (1914). (10) Hildebrand. “Solubility,” P . 94, Chemical Cataloa.. Co... New York. 1924. Hodgeman and Lange, Handbook of Chemistry and Physics, 10th ed., Chemical Rubber Publishing Co., Cleveland. Hoffman, Bey., 22, 701 (1889). E x c . C H E M . , 21, 477 (1929). Keyes, IND. Keyes, Taylor, and Smith, J . Math. Phys., Mass. I n s f . Tech., 1 (1922). Keyes, Townshend, and Young, I b i d . , 1, 243 (1922). Olsen, Van Kostrand’s Chemical Annual, 6th ed., D. Van Xostrand Co., New York. Schneider, University of Texas, 2vI.A. Thesis, 1928. Stiles and Felsing, J . A m . Chem. SOC.,48, 1543 (1926). Taylor, Address before 24th Meeting of American Society of Refrigerating Engineers, December 5 t o 8, 1928. Taylor and Smith, J . A m . Chem. SOC.,44, 2450 (1922). Thompson, Chem. i\‘eu’s, 123, 204 (1921). Vincent and Chappius, Compt. rend., 103, 379 (1886). U‘alters and Loomis, J. A m . Chem. SOL, 47, 2302 (1925). Wilson, University of Illinois Eng. Expt. Sta., Bull. 146. (1) (2) (3) (4) (5) (6) (7)
