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
389
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).
iii E$;::
~ ~ ~ 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,
T
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
390
ANALYTICAL EDITION
It is evident that in general the shorter the periods of time during which the cooling unit runs or is at rest, the more constant the temperature will be. On the other hand, the longer the periods, the less will be the strain on the motor from starting. With very efficient stirring, it was found in test runs at 6' C. that the refrigerating unit ran for a period of about 3 minutes and was at rest for a somewhat longer period. The variation in temperature under these conditions did not exceed +0.015' and was usually within =tOo.0lo. By stirring less violently, by means of the solubility apparatus, the motor ran in periods of about 7 minutes and the variation in temperature was slightly greater, possibly *0.025'. When this variation is not objectionable, the slower stirring is preferable. The toluene-mercury regulator was a t first fastened directly to the tank. Owing to vibrations from the motor, the mercury surface was kept in constant motion, and the contact between mercury and platinum wire was continually inter-
Vol. 3, No. 4
rupted, causing the motor to run erratically. This wai corrected by fastening the regulator to a support which was not connected with the tank. The shape of the platinum tip making the connection a t the mercury surface was also found important in causing the motor to start and stop promptly. A smooth, flat point was found preferable to a needle pointq2 The special apparatus used in the construction consisted of a Kelvinator Condensing Unit L-53, a small relay running on direct current, and a larger Westinghouse relay running on alternating current. By suitable modifications in the wiring and the use of a heating coil, the apparatus can be used for high temperatures as well as low. The writers are particularly indebted to Professor Herbert S. Harned of this laboratory for advice and suggestions regarding the thermostat.
* The referee has suggested that a nickel wire might make a better contact than platinum, as the former is not wetted by mercury.
Determination of Iron in Milk and Other Biological Materials' Ralph Stugarf REEDAND CARNRICK,JERSEY CITY,N. J.
Methods employing large quantities of potassium or The iron content of milk and milk powder reported by various authorities varies widely, and this variation can be sodium hydroxide are unsatisfactory for the determination traced not so much to the contamination of the milk as to of very small amounts of iron. Potassium or sodium the methods of analysis employed and to the procedure hydroxide cannot be freed from iron by allowing a 40 per cent solution to stand several days and decanting the in preparing the material for analysis. The colorimetric method using ferrocyanide cannot be clear solution. Correction for the iron in the potassium used in the presence of appreciable amounts of phosphorus and sodium hydroxide is unsatisfactory owing to the fact that the iron is not completely precipitated, and blank and calcium. The sulfocyanate method employing amyl alcohol for determinations are unreliable because of the varying extracting the ferric sulfocyanate is reliable. The deter- proportions of iron precipitated. Methods using small quantities of alkali are unreliable mination involving the comparison of aqueous solutions is not permissible owing to the fading of the color. The due to the presence of iron in the sodium hydroxide use of ether for extracting the iron sulfocyanate is not and to the iron dissolved from the glass during heating. satisfactory and acetone does not afford a guarantee The results may indicate several times as much iron against fading. The iron content of milk cannot be deter- as actually present. A method in which alkali treatment is eliminated and the mined with sufficient accuracy by gravimetric or voluiron determined as ferric sulfocyanate is given in detail. metric methods. .. . . .. ., ., .. . . HE accurate determination of iron in milk has acquired greater importance on account of the recent work on nutritional anemia. As reported in the literature, the iron content of milk varies widely, but in an excellent review of the subject, Nottbohm and Weisswange (21) point out that this variation should be attributed less to the milk itself than to the inaccuracy of the method of analysis. This statement seems to apply also to the more recent data. Herapath (9) was the first to take advantage of the color of ferric sulfocyanate for the determination of small amounts of iron. Later, Thompson (26) used the same method with slightly different procedure and the method is frequently referred to as Thompson's method. Zega (27) used sulfocyanate for the determination of iron in water and stated that hydrochloric acid was not so good as nitric acid for acidifying. Mai (15) and Soxhlet (28) employed this method in determining iron in milk. Andrews (1) found that solutions in
T
1 Received April 16, 1930. Presented before the Division of Medicinal Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930.
ethyl ether, amyl alcohol, and absolute ethyl alcohol were more intensely colored than aqueous solutions, indicating that dissociation or hydrolysis was responsible for the lighter color and the fading of aqueous solutions. Moore (18) noted that potassium sulfocyanate could not be used as a qualitative test for iron in the presence of phosphoric acid. In the determination of iron in milk, Ewers (6) found it necessary to remove the phosphates from the milk ash, and also observed that sulfocyanate could not be used in the presence of pyrophosphates. Elvehjem and Hart (5) removed the interfering phosphates from milk ash but made no attempt to overcome the error due to fading in aqueous solutions. Ether was first used by Natanson (19) to make the test for iron with sulfocyanate more sensitive. Tatlock (25) used ether as a solvent for ferric sulfocyanate in the determination of iron in alum. Von K6ler and Lunge (10) used the procedure of Tatlock and pointed out that the determination involving the comparison of aqueous solutions was not permissible, owing to the fading of the color. Lachs and Fried-
