Chemical Analysis of Milk and its Products. 211 



represents .03129 grams of nitrogen. This quantity of nitrogen 

 was obtained from the 5.1465 grams of milk measured out; the 



milk therefore contains ^^~=.608 per cent, of nitrogen, 

 and .608X6.25=3.80 per cent, of casein and albumen. 



254. Casein and albumen may be determined separately 

 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 3-5 minutes. The 

 whey is decanted through a filter and the precipitate 

 washed two or three times with cold water. The nitro- 

 gen 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 multiplied by 6.25 

 gives the per cent, of casein in the milk. 



255. Albumen is determined in the filtrate from the 

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

 and heated to boiling temperature of water for 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 between 

 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). 



1 Bulletin No, 43, p. 189, Chemical Division, U. S. Dept. of Agriculture. 



