314 Report of the Department of Chemistry of the 



In our previous work we have shown that 1 gram of uncombined 

 casein combines with 9 x 10 -4 gram equivalents of calcium to form 

 a salt that is neutral to phenolphthalein. 1 In column 2 of Table IV 

 we make use of this fact in calculating the acid equivalents of the 

 casein as found in each sample. In column 3 of the same table, 

 we calculate the acid equivalents of the insoluble inorganic phos- 

 phorus in each sample of milk (regarding phosphoric acid as a di- 

 valent acid and CaHP0 4 neutral to phenolphthalein). In column 

 4 are shown the sums obtained by adding the figures in columns 2 

 and 3 in case of each sample of milk. In columns 5 and 6 are given 

 the combining equivalents of calcium and magnesium and in column 

 7 their sum for each sample of milk. If now we compare, in case of 

 each milk, the figures contained in column 4 with those contained in 

 column 7, we notice that they are in close agreement, the differences 

 being shown in column 8. This agreement means that the quanti- 

 tative relation between the bases (calcium and magnesium) and 

 the acids (casein and phosphoric acid) is that required, theoreti- 

 cally, to give di-calcium phosphate with a trace of di-magnesium 

 phosphate and calcium caseinate neutral to phenolphthalein, in 

 which casein is combined with 8 equivalents of calcium (casein 

 Ca 4 ). However, the same analytical figures can with equal correct- 

 ness be interpreted to prove that the compounds are present as acid 

 caseinate and tri-calcium phosphate. 



In order to decide which of these sets of compounds is present in 

 milk, we have tried to make a separation of the casein and insoluble 

 phosphates. The above results, it will be remembered, are obtained 

 by difference, the milk and serum being analyzed and the composition 

 of the insoluble portion being determined by subtracting the latter 

 results from the former. It seemed desirable to separate milk in 

 large amounts so as to obtain the insoluble portion in quantity 

 sufficient to purify and analyze. This was done in the following 

 manner, several experiments being made. In the first experiment, 

 400 pounds of milk was run through a centrifugal cream separator 

 18 times and the deposit (" separator slime ") collecting on the 

 walls of the bowl was removed after the 1st, the 6th, the 12th and 

 the 18th run. Each of these deposits was placed in a mortar and 

 triturated with small amounts of 95 per ct. alcohol with the gradual 

 addition of more alcohol. A point is reached when the whole mass 

 becomes jelly-like, after which the addition of more alcohol causes 

 the formation of a fine flocculent precipitate. (Care must be 

 taken not to add the alcohol too rapidly, because then there is apt 

 to be formed a tough, leathery mass, which can not be handled.) 

 The precipitate is allowed to settle and, after decanting the super- 

 natant liquid, is triturated with several successive portions of 95 

 per ct. alcohol, 99 per ct. alcohol, and finally ether. It is then dried 



4 N. Y. Agrl. Expt. Sta. Tech. Bui. No. 26, p. 12. 



