October 15, 1931
INDUSTRIAL AND ENGINEERING CHEMISTRY
I n distillations, cooling of condensers with solid carbon dioxide must be done in such a way as to prevent or minimize freezing of the distillate on the condensing surface. Water, mercury, carbon tetrachloride, and even anhydrous ammonia freeze a t “Dry-Ice” temperatures, and consequently the design of condensers for handling them must be such that freezing will not clog condensate passages or unduly reduce the heat-transfer rate a t the cold surface. An arrangement, which allows the liquid to flow readily off the condensing surface into a receiver to be further cooled, is advantageous where there is danger of freezing the distillate. A number of solvents, especially ether, alcohol, acetone, carbon disulfide, and others are still liquid a t -78.5” C. and can be easily handled through such a low-temperature condensing system. Figure 1 shows a suggested condensing system, in which a temperature of -20” C. was reached in the condenser jacket. That shown in Figure 2 produces very low temperatures, down to -78.5” C. The dehydration of low-freezing solvents by cold and the crystallization of other materials from them has already been suggested above. The technic of doing this is very simple and will readily occur to the investigator. To produce rapid cooling, a slush of solid carbon dioxide in alcohol or ether is placed in a convenient receptacle, preferably a vacuum jar (Pyrex glass), and the solution to be cooled in a convenient container is placed in the mixture. Where slower cooling is required, “Dry-Ice” in small pieces without a solvent may be used and a double-walled vessel for the solution to be cooled still further prolongs the cooling period if this is desired. The application of extreme cold in the separation of mixtures of materials of widely different freezing points in this way offers many possibilities of value. The removal of fat8
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from alcohol solutions of perfume concretes has been commercially practiced for some time. The separation of benzene from a mixture with ether and many other similar operations can be readily accomplished by crystallization a t very low temperatures. The use of solid carbon dioxide a8 a condensing or carboncooling agent in the production of high vacua with mercurydiffusion pumps is more convenient and cheaper than the use of liquid air and is being widely adopted. Dehydration of gases to an extent attainable only by the most careful use of chemical dehydrating agents, and the separation of many low-boiling hydrocarbons and other compounds from gases is conveniently accomplished by passing the gas through a glass or metal condenser cooled by solid carbon dioxide either alone or mixed into a slush with alcohol or ether. Safe storage of products sensitive to oxidation but not injured by carbon dioxide can sometimes be best accomplished by carbonation with “Dry-Ice.” Thus, some years ago samples of cracked petroleum distillate very sensitive to light and oxygen were stored in carbonated-beverage bottles, dropping into each 6-ounce sample approximately 3 grams of “Dry-Ice” before capping with an ordinary carbonated beverage crown. So far as the changes in color and gum formation would indicate, oxygen elimination was probably complete. These possibilities are outlined here to point out the convenience in laboratory practice of this commercial product and to suggest ways in which it can be usefully applied. Literature Cited (1) Evans, Cornish, and Atkinson, J . A m . Chem. SOC.,62, 4334 (1930).
Determination of Butyl and Ethyl Alcohols in Mixtures’ C. H. Werkman and 0. L. Osburn DEPARTMENT OF BACTERIOLOGY, IOWA STATE COLLEGE, AMES,IOWA
HE partition method Ethyl and butyl alcohols are readily and accurately acetaldehyde, acetoin, or ace(3-7) for the determidetermined by oxidation by potassium dichromate in tone be present in the distilnation of fatty acids in acid solution to the corresponding acids and quantitalate to interfere with the final a mixture may be applied to tive determination of the acids by the partition method. results due to oxidation to the determination of ethyl and The method is designed for quantitative determinaacetic acid, they should be rebutyl alcohols in a mixture tions of the two alcohols in fermentation liquors. moved bv DreciDitation with wit6 good results. The prosome suitatle sibstance such. cedure is simple, rapid, and accurate. The alcohols are oxi- as 2,4-dinitrophenylhydrazine as prepared by van Niel (9). dized to fatty acids with potassium dichromate in the presence For the oxidation, 50 cc. of the alcoholic distillate are placed of orthophosphoric acid. The acids are distilled and the dis- in a 200-cc. balloon flask containing 10 grams of c. P. potassium tillate partitioned between isopropyl ether and water as de- dichromate and 25 cc. of 85 per cent phosphoric acid (ortho). scribed in the partition method. From a calculation of the per- The flask must be fitted with an efficient reflux condenser, centage of acid distributed to the aqueous phase, the percent- preferably with a spiral condensing tube. A few pieces of ages of each of ethyl and butyl alcohols can be read directly from porcelain are added to prevent bumping, and the mixture the nomogram in Figure 2. This method is especially useful heated a t such a rate that it boils in 1.5 minutes. Gentle in the quantitative determination of ethyl and butyl alcohols boiling is then continued for 3 minutes. The condenser tube in fermentation liquors when either one or both are present. is washed down two or three times during the boiling with Van der Lek (1) has determined these alcohols by oxidizing 5-cc. portions of water. If the process is carefully carried out with dichromate and sulfuric acid, steam-distilling the volatile and if the condenser is efficient, no volatile constituents will acids, and then determining the acids by the method of be lost. The flask is cooled rapidly by immersing it, with the Duclaux. condenser still attached, in cold water. As soon as the is cooled to avoid loss of volatile acid, the condenser flask Procedure is again washed down with 15 cc. of water. The flask is reThe alcohols are distilled from the neutral fermentation moved and connected to a Liebig condenser, and the mixture medium by direct distillation. Should substances such as distilled until it begins to foam. There is no tendency to bump, and distillation proceeds smoothly. When the foam 1 Received March 9, 1921.
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Figure 1-Partition
ANALYTICAL EDITION
of Acetic a n d Butyric Acids between Isopropyl
Ether a n d Water Ordinates indicate per cent of each acid present; abscissas, per cent of acid in aqueous phase ( K I )
VOl. 3, No. 4
timeters of the original acid solution are titrated and the number of cubic centimeters of sodium hydroxide is recorded as M. Then P'/M X 100 = K . This K is designated as the percentage partition constant for the acid solution. These percentage partition constants have the same significance as the constants employed by Osburn and Werkman (S),but in this case the acid need not be adjusted to exactly 0.1 N . I n Figure 1, the values of K are plotted against the percentages of the acids. It is thus possible to read off the per cent of each acid from any determined value of K . If pure acetic acid is present, the value of K will be 89.0. If only butyric acid is present, the value of K will be 34.8. Mixtures of the acids give intermediate values of K . From Figure 1 the per cent of each acid can be obtained. The per cent of each alcohol can then be calculated since 1 cc, of molar alcohol, regardless of which one, gives 1 cc. of normal acid. It is more convenient to construct a diagram from which the per cent of each alcohol may be read directly. Since pure butyl alcohol gives on oxidation 90.3 per cent butyric and 9.7 per cent acetic acid, it is evident from Figure 1 that pure butyl alcohol would give on oxidation and partition a value of K = 40. If pure ethyl alcohol is oxidized, then K = 89. I n Figure 2 the values of K between 40, representing 100 per cent butyl alcohol, and 89, representing 100 per cent ethyl alcohol, are plotted against the percentages of the alcohols. An example will make clear the use of Figure 2. An unknown mixture of ethyl and butyl alcohols gives on oxidation and partition a value of K = 70.5. From Figure 2 it is seen that if K = 70.5, the alcohol in the mixture must be 62 per cent ethyl and 38 per cent butyl. The number of cubic centimeters of 1.0 M alcohol in the 50 cc. taken must be the same as the number of cubic centimeters of 1.0 N acid produced. Since the total acid produced is known, it is a simple matter to calculate the weights of each alcohol present.
which forms has risen to half the volume of the flask, heating is reduced until foaming is just maintained. If the heating Discussion is then continued for about 3 minutes, all of the organic acids but none of the phosphoric acid are distilled over. The disThe method as described is accurate for solutions which give tillate should be colorless and about 85 cc. in volume. This approximately 0.1 N acid when the distillate is made up to volume is made up to 100 cc. with distilled water. Ethyl alcohol is oxidized completely to acetic acid; butyl 100 cc. The percentage partition constants for the acidsshift somealcohol, due to @-oxidation, gives a mixture of butyric and acetic acids containing 90.3 per cent of butyric acid and 9.7 what as the acid solutions become more dilute. The method per cent of acetic. No formic or propionic acid is present. holds quite well down to about 0.05 N. If it is necessary to In order to establish this constant for butyl alcohol, several work with more dilute acids, new constants should be essolutions were oxidized containing from 50 to 600 mg. of butyl tablished to fit the conditions. The procedure as outlined should be followed in detail alcohol in the 50-cc. volume used for analysis. The constantsobtained were: 90.0,90.2,90.0,90.5, and 91.0 per cent butyric acid. The butyl alcohol was purified by repeated fractionation t h r o u g h a Y o u n g fractionating column. The middle fraction of the distillate was collected each time until a fraction with a c o n s t a n t boiling point of 117' C. was obtained. This fraction was f u r t h e r redistilled until a constant oxidation factor was obtained. Thirty cubic centimeters of the acid solution, approximately 0.1 N, are shaken for 1 minute in a separatory funnel with 20 cc. of isopropyl ether a t 25' C. After 3 minutes, 25 cc. of the water layer are withdrawn and titrated with 0.1 N sodium hydroxide* The cubic centimeters Figure 2-per C e n t of Butyl and Ethyl Alcohols from Percentage Partition C o n s t a n t s Of of sodium h y d r o x i d e required are reCorresponding Acids Abscissas indicate percentage partition constants ( K ) corded as P'. Twenty-five cubic cen-
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INDUSTRIAL A N I ) ENGINEERING CHEMIXTRY
October 15, 1931
sine$ changing the concentration of the oxidizing constituents causes considerable change in the ratio of acetic t o butyric acid. The manner of heating the mixture may also cause a slight variation in the acid ratio. This is in substantial agreement with the results obtained by van der Lek ( I ) . If isopropyl alcohol is present, it will be oxidized to acetone. The oxidation does not stop a t acetone but goes on to acetic acid. (The formic acid produced is oxidized to carbon dioxide and water.) It is estimated that 5 to 10 per cent of the acetone so produced is oxidized. Small quantities of acetone do not interfere with the partition method. Isopropyl alcohol is infrequently present in fermentation liquors and then only in traces. If acetone is produced, it can be precipitated from an aliquot with 2,4-dinitrophenylhydrazine and the isopropyl alcohol can be estimated. If acetone is present in the original alcohol solution, it should be precipitated and filtered. The filtrate should be made alkaline with sodium hydroxide and the alcohols distilled. Characteristic analyses are reported in Table I.
Table I-Results ALCOHOL TAKEN Ethyl
Butyl
%
%
69.0 69.0 82.3 82.3 100 69.9
31.0 31.0 17.7 17.7
3o 0 0
30 4
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of Analyses of Alcohol Mixtures ALCOHOL FOUND
K
Ethyl
I l
0
30.1 100 7o 100 70
Total normality
TOTAL ALCOHOL
Butyl
% 99.8 98.0 99.5 97.5 97.0 96.5 99 100 100 98.8
acid produced was only 0.02.
Literature Cited (1) Lek, van der, “Onderzoekingen over de butylalkoholgisting,” Thesis, Delft, 1930. (2) Niel, van, “The Propionic Acid Bacteria,” Thesis, Delft, 1928. (3) Osburn and Werkman, IND. ENG.CHEM.,Anal. Ed., 3, 264 (1931).
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~ ~ ~ i ~ ; ~ ‘ o ~ ~ 4, ~ 459 . o ~(1930). c i . , Werkman, Ibkd., 5, (1930). (7) Werkman, I b i d , , 5, 121 (1930).
A Low-Temperature Thermostat’ H. W. Foote and Gosta Akerlof DEPARTMENT OB CHEMISTRY, YALEUNIVERSITY, NEWHAVEN,CORN.
HE thermostat described below is the outcome of an attempt t o use a regulated cold supply, from a small electric refrigerating unit, to maintain a constant low temperature in the same way that a regulated heat supply is used to maintain a constant high temperature. The thermostat has been in continuous use for several months and appears to run equally well a t any temperature between the minimum room temperature and 0” C. It has not been tested below the latter. The variations in temperature can, if desired, be kept within *0.015”, and the apparatus requires no more attention when running than the ordinary electrically heated thermostat,
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Figure 1-Diagram
control is required. The tank is lined with tinned copper and is heat-insulated with two layers of “insulite” between the metal and wood. Horizontal cleats run about the outside of the tank through which run upright iron rods for holding equipment. The cover is in sections so that a part of the tank can be uncovered without undue heat exchange with the surroundings. A diagrammatic wiring plan for regulating the temperature is shown in Figure 2. At A , a d. c. potential of 110 volts allows a constant small current to pass through a fixed resistance of 750 ohms. From this resistance, a small current of about 5 milliamperes, which passes to the regulator B and. activates a small relay, C, is tapped. This relay was not capable of carrying the current necessary for the cooling unit, and therefore a second rather heavy relay which could be used on an alternating current was used, and the cooling unit D was placed in the circuit as shown.
of Low-Temperature T h e r m o s t a t
The apparatus consists essentially of a tank (Figure 1)holding about 450 liters. At one end, the cooling unit, consisting bf a ‘/,-horsepower motor and compressor, rests on the lower shelf. A copper tube, about 60 feet (18.28 meters) long, containing the refrigerant leads through a valve, not shown in the diagram, into the tank and is coiled around the inside on a wooden frame. The motor on the upper shelf a t the right is connected with a stirring apparatus as indicated. The apparatus a t the left is for solubility determinations, and when in use provides sufficient stirring so that the other stirrer is not used unless exceedingly close temperature 1
Received May 8, 1931.
Figure 2-Wiring
Diagram
