102 MILK PRODUCTS 
on which is placed a mixture containing equal 
parts of anhydrous copper sulfate and pure dry 
sand to the depth of about 5 cm., packed loosely, 
and the upper surface covered with a film of 
asbestos. On this are placed from 2 to 5 grams 
of the sample, the mass extracted for five hours 
with anhydrous ether, then removed and ground 
to fine powder with pure sand in a mortar. The 
mixture is replaced in the extraction tube, the 
mortar washed free from all matters with ether, 
the washings being added to the tube, and the 
extraction is continued for tenhours. The fat so 
obtained is dried at 100? to constant weight. 
Here, as in most extractions, carbon tetra- 
chiorid can be substituted for ether, but the 
results obtained are not necessarily equivalent, 
and in official analyses the official method must 
be used. 
Total Nitrogen.—This is determined by the 
Kjeldahl-Gunning method, using 2 grams of the 
sample. The percentage, multiplied by 6.38, 
gives the nitrogen compounds. 
Ash.—The dry residue from the water de- 
termination may be taken for the ash. If the 
cheese is rich, the asbestos will be saturated there- 
with. This mass may be ignited carefully, and 
the fat allowed to burn off, the asbestos acting as 
a wick. No extra heating should be applied 
during the operation, as there is danger of spurt- 
