CASEIN. 177 



Estimation of Casein. Lehmann's Method. Lehmann has 

 devised a method for the estimation of casein in milk by 

 means of unglazed porcelain plates ; the plate is wetted with 

 water, and 5 grammes of milk diluted with 5 grammes of water 

 placed in the centre. After about an hour and a half the serum 

 is separated, and the casein, together with the fat, is removed 

 with a spatula ; the last traces of casein .are removed by setting 

 the plate in water. The fat is removed by extraction with 

 ether, the casein being ground up to extract the last traces ; the 

 casein is dried at 100 C. on a weighed filter, and weighed ; 

 from the weight is deducted the weight of the ash left on 

 incineration. 



The results are said to be very accurate. The casein is 

 obtained in the state in which it exists in the milk. 



Schlossman's Method. Schiossman proposes estimating 

 casein by warming 10 c.c. of milk mixed with 3 to 5 parts of 

 water to 40, and adding 1 c.c. of a concentrated solution of 

 alum. Should the flocculent precipitate not subside rapidly an 

 additional 0-5 c.c. of alum solution may be added, since a slight 

 excess (up to 1 c.c.) does not affect the results. The precipitate 

 is allowed to stand for some minutes, and is then filtered. After 

 having been washed with water and dried, the filter and its 

 contents are extracted with ether in a Soxhlet extractor (an 

 estimation of fat being thereby obtained) ; the nitrogen deter- 

 mined by Kjeldahl's method, and multiplied by 6-39, gives the 

 weight of the casein. 



Richmond's Method. The albumin in milk, which has been 

 raised to the boiling point, behaves with all methods as casein. 

 An approximate estimation of real casein in milk, which has been 

 heated, can be made as follows : Twenty-five grammes of milk 

 are evaporated to dryness, ignited, and the phosphoric acid 

 estimated in the ash, as directed on p. 228. Twenty-five c.c. of 

 the filtrate, produced by adding 3 c.c. of acid mercuric nitrate to 

 100 c.c. of milk, are taken, evaporated down, and ignited ; the 

 phosphoric acid is estimated in the ash. 



The casein is calculated from the following formula : 



Let P x = P 2 5 obtained from 25 grammes of milk, 

 P 2 = P 2 O 5 obtained from 25 c.c. of filtrate, 

 F = percentage of fat, 

 and S = the specific gravity. 



Then casein = (P x - P 2 X "g 1 ' 1 ^) X 205-2. 



The coagulated albumin is deducted by subtracting this figure 

 from the apparent percentage of casein estimated by one of the 

 methods previously described. 



The Volumetric Determination of Casein in Milk. Van Slyke 



12 



