Chemical Analysis of Milk and Its Products. 223 



for two to three hours, and weighed. This method is 

 applicable to new milk, skim milk, butter milk, whey, 

 cream, cheese, condensed milk and milk powder, but has 

 been found of special value for determining fat in skim 

 milk, butter milk, cheese, and condensed milk. In the 

 case of products high in fat, a second treatment with 

 10 cc. each of ether and petroleum is advisable in order 

 to recover the last traces of fat. 



255. d. Casein and albumen. The sum of these com- 

 ponents is generally determined by the Kjeldahl 

 method. 1 5 cc. of milk are measured carefully into a 

 800 cc. Jena flask, 20 cc. of concentrated sul- 

 furic acid (C. P. ; sp. gr., 1.84) are added, and .7 gram 

 of mercuric oxid (or its equivalent in metallic mer- 

 cury) ; the mixture is then heated over direct flame 

 until it is straw-colored or perfectly white; a few crys- 

 tals of potassium permanganate are now added till the 

 color of the liquid remains green. All the nitrogen in 

 the milk has then been converted into the form of am- 

 monium sulfate. After cooling, 200 cc. of ammonia- 

 free distilled water are added, 20 cc. of a solution of 

 potassium sulfid (containing 40 grams sulfid per liter), 

 and a fraction of a gram of powdered zinc. A quan- 

 tity of semi-normal HCl-solution, more than sufficient 

 to neutralize the ammonia obtained in the oxidation of 

 the nitrogen in the milk, is now carefully measured out 

 from a delicate burette (divided into -fa cc.) into a re- 

 ceiving flask and the flask connected with a distillation 

 apparatus. At the other end, the Jena flask containing 



l Fresenius' Zeitschrift, 22, p. 366; U. S. Dept. Agr., Bur. of Chem., 

 Bull. 107, p. 5. 



