Chemical Analysis of Milk and Its Products. 223 



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 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 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 be- 

 tween the total nitrogenous components found by the 

 Kjeldahl method, arid 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). 



258. Hart's test for casein in milk. The folllowing 

 test for casein in milk has been published by the Wis- 

 consin experiment station r 1 



Two cc. of chloroform, 20 cc. of a .25 per cent, solu- 

 tion of acetic acid, and 5 cc. of milk (both these latter 

 of a temperature of about 70 F.) are measured into 

 small tubes of special construction holding about 35 cc., 



1 Report 24, p. 117: "A simple method for the estimation of casein 

 in cow's milk," by E. B. Hart. 



