72 MILK ANALYSIS 



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 precipitate 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 precipi- 

 tate 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 per cent, water and 

 10 per cent, glycerol in sufficient quantity to obtain a uniform 

 magma that can be measured with a pipet. The quantity of 

 copper hydroxid per c.c. should be determined. It should be 

 kept in a well-closed bottle. 



Ammonium Compounds. About 5 grams of cheese are 

 rubbed up in a mortar with water, transferred to a filter, and 

 washed with a liter of cold water. The filtrate is concentrated 

 by boiling (if alkaline, it must be neutralized before heating), 

 barium carbonate added, the liquid distilled, and the ammo- 

 nium hydroxid in the distillate estimated by titration with stan- 

 dard acid. 



According to Stutzer, magnesia or magnesium carbonate 

 (the latter usually contains some magnesia) should not be used 

 to free the ammonia, as some of the amido-compounds may 

 be decomposed. 



Amido-compounds. The nitrogen as amido-compounds is 

 estimated by subtracting from the figure for total nitrogen the 

 sum of the proteid and ammoniacal nitrogen. If nitrates are 

 present, the nitrogen as such should also be determined and 

 subtracted. 



Van Ketel & Antusch propose the following methods for 

 estimating the nitrogen compounds: 



Ammonium Compounds. The sample, powdered with the 



