122 



Citric acid as a normal constituent of cows' milk, T. Henkel 



[Landic. Vers;. Stat., 39. pp. 143-151 ). — The author ])refa('es the report of 

 his investigations with a brief summar3' of the substances besides albu- 

 minoid materials, fat, milk sugar, and ash, which, according to present 

 views, occur in small quantities in normal milk. Of nitrogenous bodies 

 other than the albuminoids, he mentions urea, ammonia, hypoxanthin, 

 and lecithin. The old theory that i)eptones are contained in milk, is 

 believed to have been disproved by more recent investigations.* 

 Among the nitrogen-free materials of the milk he recogin"zes cholesterin. 



Regarding the organic acids of milk, Soxhlett tirst remarked that the 

 amount of lime contained in solution in milk seemed to be opposed to 

 the fact that milk contains phosi>horic acid in solution. He suggested 

 the presence of an "organic ])hosphoric acid" whose neutral calcium 

 salt was soluble. Soldner | in his work on the salts of the milk, further 

 advocated the presence of organic acids in milk. According to 

 Ileidlen,§ lactic acid is not a constituent of fresh milk, and only occurs 

 in milk which has stood. The author states that the only previous 

 mention of the actual finding of an organic acid in fresh milk is by 

 I)uval,|| who stated that he found the salt of such an acid in mares' milk. 

 This salt, as described, crystallized iu groups of small needles, was not 

 volatile, gave a peculiar odor on heating, and dilfered from hippuric 

 acid in its relation to silver nitrate and iron chloride. He named this 

 acid acule equinique. 



The present investigations were made by the author under the super- 

 vision of Professor Soxhlet, at the Central Experiment Station in 

 Munich. It seemed i)robable from all previous investigations that the 

 organic acids if present must be contained in the milk serum in the 

 form of soluble salts. A serum was prepared from separator skim milk 

 by removing the casein, first with a strong rennet solution and then with 

 acetic acid and Spanish clarifying earth (Klarerdc). and neutralizing with 

 milk of lime to the i)oiut of acidity of normal milk serum (100 c. c. = 3. 2 

 c. c. fourth-normal soda solution). By this means a clear milk serum 

 of normal acidity was obtained. On evaporation of the serum a pre- 

 cipitate separated out, which was found by (|ualitative tests to be the 

 calcium salt of an organic acid, contaiuing also a small admixture of 

 calcium phosphate. This organic acid was obtained free (1) bydecom 

 posing the calcium salt with oxalic acid, aiul (2) bj' preparing the lead 

 salt and decomposing it with hydrogen suiphide. When i)uritied and 

 concentrated both these solutions gave a crystalline mass. Larger 

 quajitities of the pure acid were prepared by decomposing the calcium 

 salt with II2SO4, dehydratiug with anhydrous gypsum, placing over 



* Jabrcsber. f. Thier Chera., 6.13; Zeitach. f. pbysiol. Cbem., 2, 28; ibid. 9, 591. 

 t Jour. f. prak. Cbera., 6, 1. 

 t Landw. Vers. Stat., 35, 354. 

 $A""- '1- Cbem. n. Pbysik., 45, 263. 

 II Coiupt. reud., 82, 419. 



