ANALYTIC PROCESSES 31 
Kjeldahl-Gunning method. The nitrogen, multi- 
plied 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°, 1 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. 
