I06 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). — 0.7 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 and 10% 

 glycerol in sufficient quantity to obtain a uniform 



