Kew York Agricultural Experiment Station. 321 



reaction was completely removed. The resulting solution, con- 

 taining mono-ammonium caseinate, was then precipitated by addi- 

 tion of acid-free alcohol. The precipitate was filtered, washed with 

 acid-free alcohol and ether and dried at 120° C. In several prepara- 

 tions thus made the amount of ammonia was determined; the results 

 are given in the following table: 



Table V. — Composition of Mono-ammonium Caseinate. 



♦Preparations of caseinatea made by Mr. O. B. Winter. 



Acid casemates of calcium, strontium and barium. — In making 

 preparations of the caseinates of the alkaline earth bases, difficulty 

 was experienced in obtaining concordant results. The trouble was 

 finally found to be due to the presence of the chloride formed when 

 the solution of the caseinate is treated with hydrochloric acid. Such 

 chlorides tend to cause precipitation of the caseinates either by 

 decreasing their solubility or, perhaps, by formation of double salts, 

 consisting of the chloride in combination with the caseinate.^ The 

 difficulty of insolubility is readily overcome by removal of the 

 chloride through simple dialysis before the amount is sufficient to 

 cause precipitation. To accomplish this, we made use of the fol- 

 lowing process: In 200 cc. of ^ hydroxide of calcium, strontium or 

 barium, we dissolved 5 grams of casein and then diluted the solution 

 to 250 cc. A preliminary or trial determination was made by adding 

 6u^ HCl to 50 cc. of the caseinate solution in portions of 5 cc. at a 

 time, agitating constantly and, after each addition, testing for the 

 presence of a precipitate by centrifuging a portion, until a precipi- 

 tate appeared, just as in the case of preparing alkaline caseinates 

 (p. 319). Then to each of several flasks containing 50 cc. of the 

 caseinate solution we added an amount of ^ HCl that was 5 cc. 

 less than the amount causing the first appearance of a permanent 

 precipitate in the preliminary trial. The contents of the flask were 

 then placed in dialyzing tubes and, by frequent changes of the sur- 

 rounding water, most of the soluble chloride that had been formed 

 was removed. The contents of one tube were then used for another 



1 Pfeiffer and Modelski, Ztschr. Physiol. Chem., 81: 329, 1912. 

 11 



