32() IvKPoKT oi' TiiK 1)kpakt.a!e.\t OF Chp;mistrv of the 



to be nearer the truth, owing to the difficulty of preparing these 

 caseinates in pure form. The values by the volumetric method are : 

 1 gram of casein to 1.10 (to 1.15) x 10"^ gram equivalents of cal- 

 cium for the mono-basic caseinate, and 1 gram of casein to 2.2 (to 

 2.3) X 10"^ gram equivalents of calcium for the di-basic caseinate. 



VALENCY OF CASEIN MOLECULE AND MOLECULAR WEIGHT OF CASEIN. 



In the case of the compound of casein and calcium, which is neutral 

 to phenolphthalein, it is found that 1 gram of casein combines with 

 9 X 10'^ gram equivalents of calcium. In the case of the mono- 

 ammonium caseinate, the combination is in the proportion of 1 gram 

 of casein to a value between 1 . 1 x 10"' and 1 . 15 x 10"^ gram equiva- 

 lents. Since we have one compound of known composition and 

 another of approximately known composition, it should be possible 

 by applying the rule of constant proportions to determine the true 

 composition of the mono-basic caseinate and also the number of 

 valencies satisfied in the caseinate neutral to phenolphthalein. 



We have reason to believe that the proportion, 1 gram of casein 

 to 1.125 X 10'^ gram equivalents of alkali, is the true value, since, 

 first, this lies between the two limits (1 . 10 and 1 . 15) found in our 

 volumetric work, and, second, this figure agrees with that found by 

 assuming a valency of 8 for the basic calcium caseinate, in which 

 1 gram of casein combines with 9 x 10^ gram equivalents of calcium. 

 Thus, if the valencies satisfied are 8, the proportion becomes 1 gram 

 of casein to 1 . 125 x 10'^ gram equivalents of alkali for mono-basic 

 caseinates. If, however, we were to assume that the number of 

 valencies in the basic compound is 7 rather than 8, then the mono- 

 basic salt would, theoretically, have the composition, 1 gram of 

 casein to 1.285 x 10"^ gram equivalents of alkali, a value too high 

 for our analytical results. If, on the other hand, we w"re to assume 

 the number of valencies in the basic compound to be 9, then the 

 proportion in the mono-basic compound would become 1 gram of 

 casein to 1 x 10"* gram equivalents of alkali, a value too low for 

 our analytical results obtained with mono-ammonium and other 

 alkali caseinates. Assuming 8 as the true valency of basic calcium 

 caseinate gives us the value, 1 gram of cavsein to 1 . 125 x 10 ^ gram 

 equivalents of alkali, a result which agrees with the volumetric 

 results obtained in case of the mono-alkali caseinates. 



If we use the sulphur content as a basis for calculating the mole- 

 cular weight of casein we have n(-o-7-2-) 100 = n 4454-}-. Here the 

 value of n appears to be 2, and the molecular weight would be 8908, 

 which is in very close agreement with the value found above, 

 8888+. This would indicate that there are two atoms of sulphur in 

 each molecule of casein. 



The amount of phosphorus in casein was found to be 0.71 per ct., 

 which would lead to the molecular weight, n(^o"7°i") 100 = n4372 — . 

 If the value of n is 2, the molecular weight of casein becomes 8744. 



