DETERMINATION OF ALBUMINOID NITROGEN. 47 



tion of the albuminoid bodies, and the determination of 

 the nitrogen in the precipitate by the Kjeldahl process. 

 A determination of the nitrogen in the fihrate gives the 

 so-called nitrogenous extract or non-albuminoids. 



In order to precipitate every trace of albuminoids from 

 the milk sample, any one of the following substances may 

 be used : Tannin and sodium chloride in the cold (Se- 

 belien's process), copper hydroxide in a boiling solution 

 (Ritthausen-Stutzer), or trichloracetic acid in the cold 

 (Hondsczinsky). 



/. Precipitation with Tannin. 



In a 250 c. c. beaker, 10 c. c. of milk are diluted with 

 yo c. c. of water and treated w ith about 5 c. c. of a sat- 

 urated acjueous solution of sodium chloride,* and an 

 excess of tannin or of Almen's solution (5 grams tannin ; 

 5 c. c. acetic acid, 50 per cent ; and 200 c. c. alcohol, 30 to 

 50 per cent). The resulting precipitate settles quite 

 C|uickly from a clear yellow supernatant fluid, free of 

 albuminoids. The liquid is decanted upon a small Swed- 

 ish filter and the precipitate washed repeatedly by de- 

 cantation with distilled water, and finally transferred to 

 the filter. The precipitate should be washed until the 

 filtrate shows no reaction for chlorine. Acidify a few 

 drops of the filtrate with nitric acid and add a drop or 

 two of silver nitrate, when if no turbidity ensues, the 

 washing may be considered complete. To entirely re- 

 move the soluble matter by washing requires considera- 

 ble time because the precipitate quickly fills the pores of 

 the paper, allowing the water to percolate but slowly. 

 This difficulty may be largely overcome by washing the 

 precipitate thoroughly by decantation. The precipitate. 



*In all kinds of milk, and especially in human milk, the addi- 

 tion of salt is necessary in order to effect a complete precipita- 

 tion by the tannic acid. 



