New York Agriofltural Experiment Station. 311 



casein combines with about i.i x lo"^ gram equivalents of hydroxides 

 to form insoluble compounds, which are soluble in 5 per ct. solution 

 of chloride of sodium, ammonium or potassium. This solubility is 

 due to an exchange of bases; for example, insoluble mono-calcium 

 caseinate is changed by treatment with solution of NaCl into soluble 

 mono-sodium caseinate and CaCl2, as shown by special experiments. 

 Special preparations were made of mono- and di-calcium casein- 

 ates, each compound being isolated and prepared in dry form. 

 These were found to have essentially the composition called for by 

 the previous results obtained with the volumetric work. 



(6) Valency of casein molecule and molecular weight of casein. — 

 On the basis of the composition of the basic calcium caseinate and 

 mono-calcium caseinate, the former has a valency of 8. These 

 relations indicate the molecular weight of casein to be 8888 

 and the equivalent weight mi. 



(7) Method of preparing paracasein. — Separator skim-milk is 

 heated to 37° C. and treated with 0.12 cc. of rennet-extract (Han- 

 sen's) per 1,000 cc. of milk. The milk is allowed to stand until 

 completely precipitated. The resulting curd is broken up by vigorous 

 stirring, the whey removed and the precipitated paracasein washed 

 freely with water. It is then dissolved in dilute NH4OH, reprecipi- 

 tated with acid and the operation continued and completed as in 

 case of casein. 



(8) Preparation and composition of basic calcium paracaseinate. — 

 By the same methods of study, paracasein was shown to form with 

 calcium a paracaseinate similar in composition and properties to 

 that of basic calcium caseinate. 



(9) Acid or unsaturated paracaseinates of ammonium, sodium 

 and potassium. — In these compounds, i gram of paracasein com- 

 bines with an amount of alkali somewhere between 2.2 x 10"* and 

 2.3 X 10 * gram equivalents in forming soluble compounds with 

 ammonium, sodium and potassium, which are acid to both litmus 

 and phenolphthalein. One cc. of alkali combines with 0.435 to 

 0455 gram of paracasein. The percentage of basic element in 

 each compound is, NH4 0.40; Na, 0.52; and K, 0.88. The amount 

 of each basic element in these paracaseinates is just twice that 

 present in the corresponding casein compounds. 



A preparation of mono-ammonium paracaseinate in dry form gave 

 results agreeing fairly well in composition with the results obtained 

 by volumetric work. 



(10) Acid or unsaturated paracaseinates of calcium, strontium and 

 barium. — Mono- and di-basic paracaseinates were prepared in the 

 same manner as the corresponding caseinates and were shown to 

 differ from them in having just twice as much of the basic element. 

 In the mono-basic compounds, which are insoluble, i gram of para- 

 casein combines with about 2.3 x 10^ gram equivalents of hydroxide 

 of calcium, etc.; in the di-basic, which are soluble, with about 



