106 MILK PRODUCTS 
petroleum added and the analysis carried out 
as described on page 72. 
Lactose.—This may be estimated by boiling the 
finely divided cheese with water, filtering, and 
determining the reducing power of the filtrate 
on Fehling’s solution. 
Determination of Albuminoid Nitrogen (Stutzer’s 
Method).—o.7 to 0.8 gram of the cheese are 
placed in a beaker, heated to boiling, 2 or 3 c.c. 
of saturated alum solution added to decompose 
alkaline phosphate, then copper hydroxid mix- 
ture (see below) containing about 0.5 gram of 
the hydroxid, and stirred in thoroughly; when 
cold, the mass is filtered, washed with cold water, 
and, without removing the precipitate from the 
filter, the nitrogen determined by the Kjeldahl- 
Gunning method. Before distillation, sufficient 
potassium sulfid solution must be added to pre- 
cipitate the copper. 
The special reagent is prepared as follows: 
100 grams of copper sulfate are dissolved in 5000 
c.c. of water, 25 c.c. of glycerol added, and then 
a dilute solution of sodium hydroxid until the 
liquid is alkaline. The mass is filtered, the 
precipitate is mixed well with water containing 
5 c.c. of glycerol per liter, and washed until the 
washings are no longer alkaline. It is then 
rubbed up with a mixture of 90% water and10% 
glycerol in sufficient quantity to obtain a uniform 
