CHEMICAL DYNAMICS OF ANIMAL NUTRITION 133 



EXPERIMENTS 



Determination of non-precipitable nitrogen in a mixture of sheep's 

 serum and 10 per cent, solution of Witte's peptone after precipitating 

 with tannic acid (HedinV solution). The nitrogen estimated in an 

 aliquot portion of the filtrate. 



Series I 



N in filtrate 



In experiments a, b^ c, d, the peptone solution was added to the 

 diluted serum before adding the tannic acid. In (i) tannic acid was 

 added to the serum before the peptone solution. These experiments 

 shew that the amount of residual nitrogen obtained varies with the 

 concentration of the solution in which the precipitation is carried out. 

 Series II. Same as I, with another serum, and another 10 per 

 cent, peptone solution. The total N is represented by the following 

 numbers : (a) 24-0, () 26*0, (c} 27-9, (d*) 28-6. 

 Series III. With trichloracetic acid precipitation. 



(a) 25 c.c. serum + 25 c.c. water + 5 c.c. peptone solution. 

 The mixture was then boiled. 25 c.c. of 10 per cent, 

 trichloracetic acid were then added to the mixture 

 whilst still hot. Filtrate was washed with hot water ; 

 it was then removed from paper and washed again with 

 hot water. Nitrogen estimated in total washings. 



Result : 



N = 49-0 c.c. -H 2 so* 



IO 



(^) 25 c.c. serum + 75 c.c. water + 5 c.c. peptone solution. 

 Boiled. 25 c.c. trichloracetic acid solution added. 

 Manipulation as in (#). 



Result : 



N = 5 1 -8 c.c. -^HSO* 



