Chemical Analysis of Milk and Its Products. 225 



256. Casein and albumen may be determined sepa- 

 rately by Van Slyke's method; 1 10 grams of milk are 

 weighed out and diluted with about 90 cc. of water at 

 40-42 C. 1.5 cc. of a 10 per cent, acetic-acid solution 

 are then added ; the mixture is well stirred with a glass 

 rod and the precipitate allowed to settle for 3 to 5 min- 

 utes. The whey is decanted through a filter and the 

 precipitate washed two or three times with cold water. 

 The nitrogen is determined in the filter paper and its 

 contents by the Kjeldahl method; blank determinations 

 with the regular quantities of chemicals and the filter 

 paper used are made, and the nitrogen found therein 

 deducted. The per cent, of nitrogen obtained multi- 

 plied by 6.25 gives the per cent, of casein in the milk. 



257. Albumen is determined in the filtrate from the 

 casein-precipitate ; the filtrate is placed on a water bath 

 and heated to boiling for a period of from ten to 

 fifteen minutes. The washed precipitate is then treated 

 by the Kjeldahl method for the determination of nitro- 

 gen; the amount of nitrogen multiplied by 6,25 gives 

 the amount of albumen in the milk. The difference be- 

 tween the total nitrogenous components found by the 

 Kjeldahl method, and the sum of the casein and the 

 albumen, as given above, is due to the presence in milk 

 of a third class of nitrogen compounds (18). 2 



25 7a. The protein of milk may also be obtained by 

 calculation from the total solids of the milk by the use 

 of the following formula worked out by Mr. Geo. A. 



1 Bulletin 107, p. 117, Bur. of Chem., U. S. Dept. of Agriculture. 



2 Volumetric determinations of casein in milk have been proposed 

 by Van Slyke and Bosworth (Geneva, N. Y.) expt. station, tech. bull. 

 10) and by Hart (Wis. expt. station, research bull. 11). 



15 



