DETERMINATION OF TOTAL, NITROGEN. 45 



color. Cochineal, three grams in 50 c. c. of alcohol and 

 200 c. c. of water: alkalies, especially ammonia, turn it 

 violet. Rosolic acid, two grams in one liter of 50 per cent 

 alcohol, gives with alkalines and ammonia a cherry-red 

 color. Litmus is not applicable in this analysis. The 

 residual sulphuric acid, not neutralized by the ammonia 

 distillate, is titrated with fifth-normal potassium hydrate. 

 From the number of cubic centimeters of sulpuhuric acid 

 used, that is, the number neutralized by the ammonia, the 

 nitrogen content of the milk sample may be calculated. 

 One c. c. of fifth-normal sulphuric acid is equivalent to 

 0.0034 grams of ammonia or to 0.0028 grams of nitrogen. 



From the total nitrogen found, the amount of album- 

 inoid nitrogen may be calculated by multiplying by 0.94 

 for cow's milk, or by 0.91 for human milk. Since the 

 albuminoids of the latter (casein, globulin, and albumin) 

 contain 15.76 per cent of nitrogen, the percentage of this 

 material is determined by multiplying the per cent of 

 albuminoid nitrogen by 6.34. For cow's milk the mul- 

 tiple 6.37 is used (Munk).* 



In order to make a large number of determinations by 

 this method at the same time, a variety of pieces of appa- 

 ratus have been devised (Hefter, Holbrung and Morgen, 

 Kreusler, and others). A common form of apparatus 

 for the purpose is described below. The digestion rack 

 for the treatment of the samples with sulphuric acid is 

 made as follows: a circular sheet-iron plate supported 

 ' on standards serves for the platform. Into this are cut 

 six round holes arranged in a circle. Each hole is cov- 

 ered with a wire gauze which is depressed slightly to fur- 

 nish a receptacle for the round bottom flasks. In the 

 center of the plate is placed a small iron standard which 



*Compare the details of these methods with those of the offi- 

 cial methods of the Association of Official Agricultural Chem- 

 ists. Bulletin No. 46, U. S. Dept. of .\gr.. Division of Chemis- 

 try, page 14 et seq. — Translators. 



