CHAPTER XIV 



t 



Methods of Testing Milk for Casein 



Until quite recently there have not been available 

 simple methods for the" determination of casein in 

 milk. Two methods are now in use : one of them re- 

 sembles somewhat the process used in determining 

 acidity in milk, employing the principle of neutraliza- 

 tion and titration with alkali ; while the other pre- 

 cipitates the casein and collects it by centrifugal force 

 in a graduated tube. 



VOLUMETRIC TEST FOR CASEIN 



This method was worked out at the New York 

 State experiment station (Technical Bulletin No. 10) 

 .by Van Slyke and Bosworth. In outline, the method 

 is as follows: Into a 200 cc. flask measure 17.5 cc. (18 

 grams) of milk, add about 80 cc. of water and I cc. 

 of phenolphthalein, after which run in a solution of 

 sodium hydroxide (caustic soda) until the mixture is 

 neutral. Standardized acetic acid is then added until 

 the casein is completely precipitated, the volume of the 

 mixture is made up to 200 cc. by addition of water 

 and the whole is then filtered. Into 100 cc. of the clear 



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