Chemical Analysis of Milk and its Products. 209 



is well to continue the extraction for at least 6 hours. 

 The ether is then distilled off and recovered, and the 

 flasks dried in a copper oven until constant weight; after 

 cooling they are weighed, and the amount of fat contained 

 in the quantity of milk originally weighed into the tubes 

 is thus ascertained, and the per cent, present in the milk 

 calculated. 

 Example: Weight of flask -f fat .................... 15.8039 grams. 



Weight of flask ............................. 15.5171 " 



Weight of fat ................... 2868 grams. 



Milk weighed out ............................................. 5.1232 grams. 



Per cent, of fat in milk= '^ =5.60 per cent. 



253. d. Casein and albumen. The sum of these compo- 

 nents is generally determined by the Kjeldahl method. 1 

 5 cc. of milk are measured carefully into a flat-bottom 

 800 cc. Jena flask, 20 cc. of concentrated sulfuric acid 

 (C. P. ; sp. gr., 1.84) are added, and .7 gram of mercuric 

 oxid (or its equivalent in metallic mercury); the mixture 

 is then heated over direct flame until it is straw-colored 

 or perfectly white; a few crystals of potassium perman- 

 ganate are now added till the color of the liquid remains 

 green. All the nitrogen in the milk has then been con- 

 verted into the form of ammonium 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 

 zink. A quantity of semi-normal HCl-solution, more 

 than sufficient to neutralize the ammonia obtained in the 

 oxidation of the milk, is now carefully measured out 

 from a delicate burette (divided to ^ cc.) into an 



1 Fresenius' Zeitschrift, 22, p. 366; U. S. Dept. Agr., Chern. Div., bull. 43. 

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