300 Report of the Department of Chemistry of the 

 II. THE PHOSPHORUS CONTENT OF CASEIN. 



ALFRED W. BOSWORTH and LUCIUS L. VAN SLYKE. 

 INTRODUCTION. 



In a previous paper 4 from this laboratory, a method has been 



described for preparing casein practically ash-free, the last portion 

 of calcium being removed by treating a solution of the casein in 

 dilute NH4OH with ammonium oxalate and excess of NH 4 OH, 

 and then allowing the mixture to stand about twelve hours. 

 Casein thus prepared contains about 0.71 per ct. of phosphorus. 

 The accuracy of this figure has been questioned, 5 because it is 

 considerably lower than that (about 0.85 per ct.) hitherto commonly 

 accepted as correct. The suggestion has been made that the lower 

 figure is due to the splitting off of phosphorus from the casein mole- 

 cule as the result of hydrolysis caused by prolonged contact with 

 NH4OH. 



It is the purpose of this paper to present the results of an ex- 

 perimental study relating to the effects of partial hydrolysis of 

 casein on the phosphorus content of casein preparations and also 

 to offer an explanation as to why the higher figures that have been 

 usually reported for the percentage of phosphorus in casein are 

 not correct. 



In connection with investigations recently carried on in this 

 laboratory, the results of which have not yet been published, 

 certain facts have been developed which appear to explain why 

 the high figure usually accepted for the phosphorus content of 

 casein is inevitably obtained in consequence of the method em- 

 ployed in making casein preparations. Two of the constituents 

 of cow's milk are present in the form of colloidal solution, calcium 

 casemate and dicalcium phosphate. These two compounds appear 

 to have a strong attraction for each other, as shown by the fact 

 that, when casein is separated from milk by means of either centri- 

 fugal force or precipitation with a dilute acid, the casein always 

 carries with it more or less dicalcium phosphate. It is evident, 

 then, that in preparing casein by the usual method in which care 

 is taken to avoid an excess of both acid and alkali, it is practically 

 impossible to remove this phosphate completely. In order, there- 

 fore, to ascertain the true phosphorus content of casein, it is 

 obviously necessary that the preparation be free from inorganic 

 phosphorus and this can be accomplished only by removing all 

 of the calcium. Several methods have been tried in this laboratory 

 to effect this, and the one finally found to be the most satisfactory 

 is that described in a previous paper, referred to above. 



4 N. Y. Agrl. Expt. Sta. Tech. Bull. No. 26, and Journ. Biol. Chem. 14:203. 

 1913. 

 6 Harden and Macallum. Biochem. Journ. 8:90. 



