ANALYTIC PROCESSES 3 1 



Kjeldahl-Gunning method. The nitrogen, multi- 

 pUed by 6.38, gives the casein. 



In working with milk which has been kept 

 with preservatives, the acetic acid should be 

 added in small portions, a few drops at a time with 

 stirring, and the addition continued until the 

 liquid above the precipitate becomes clear or 

 nearly so. 



2. Provisional Method for the Determination of 

 Albumin in Milk. — The filtrate obtained in the 

 above operation is neutralized with sodium 

 hydroxid, 0.3 c.c. of the 10% solution of acetic 

 acid added, and the mixture heated for fifteen 

 minutes. The precipitate is collected on a filter, 

 washed, and the nitrogen determined. 



Van Slyke has pointed out that the casein can 

 be approximately ascertained by multiplying 

 the figure for total proteins by 0.8. 



Modified Proteins, Amino-derivatives and Am- 

 monium Compounds. — The following procedures 

 are given by Van Slyke. The filtrate from the 

 albumin precipitate is heated to 70°, i c.c. of 

 5% sulfuric acid added, then solid zinc sulfate 

 to saturation. The mixture is allowed to stand 

 at 70° until the caseoses settle. The liquid is 

 cooled, filtered, the precipitate washed with 

 saturated solution of zinc sulfate slightly acidified 

 with sulfuric acid and the nitrogen ascertained 

 by the Kjeldahl method. 



