New York Agricultural Experiment Station. 301 



Further, a good reason for believing that the lower figure more 

 closely approximates the truth than the higher one hitherto com- 

 monly accepted as correct is the relation of phosphorus to the 

 molecular weight of casein. In a previous paper 6 it was shown 

 that the molecular weight of casein is approximately 8888. Now, 

 if the casein molecule contains two atoms of phosphorus, the per- 

 centage of phosphorus is 0.698, while the phosphorus content would 

 be 1.046 per ct. if there were three atoms of phosphorus. The 

 figure (0.85 per ct.) heretofore regarded as correct represents, there- 

 fore, on account of the presence of impurities in the preparation, 

 neither two atoms nor three atoms of phosphorus, while the lower 

 figure (0.71 per ct.) represents almost exactly two atoms. 



Coming now to the criticism made that an excess of NH 4 OH 

 in contact with casein for twelve hours causes hydrolysis, result- 

 ing in the formation of inorganic phosphorus, there is reason to 

 believe that, whatever hydrolysis takes place, it does not necessarily 

 interfere with the composition of the final preparation, because, 

 as will be shown, the products of hydrolysis are not precipitated 

 by dilute acetic acid and therefore form no part of the completed 

 preparation which is pure, unhydrolyzed casein. 



experimental. 



After giving the ash and phosphorus content of several prep- 

 arations of casein, we will present the results of a study of two 

 special preparations of casein which were subjected to varying 

 conditions in order to ascertain whether hydrolysis affects the 

 phosphorus content of casein preparations. 



Ash content and phosphorus content of casein. — The percentages 

 of ash and phosphorus in five samples of casein prepared in this 

 laboratory during the past seven or eight years are as follows: 



6 N. Y. Agrl. Expt. Sta. Tech. Bull. No. 26, and Journ. Biol. Chem., 14:228. 

 1913. 



