THE SCIENTIFIC FEEDING OF ANIMALS 



in chemical combination in the feeding stuffs is thereby converted into ammonia 

 which combines with the sulphuric acid. 



After completion of combustion the mass is allowed to cool, and the residue is 

 diluted by the addition of 20 cc. of water. After cooling, add 80 cc. of a solution 

 of caustic soda (free from nitric acid) and sp. gr. 1. 35; 25 cc. of 4 percent potas- 

 sium sulphid solution (to precipitate the mercury) and a few granules of zinc, and 

 connect immediately with distillation tube (Fig. 2). The latter terminates with its 

 distal end in an Erlenmeyer flask (condenser) which contains 10 to 20 cm. normal 

 sulphuric acid and sufficient water so that the end of the distillation tube dips into 

 the fluid. After about 100 cc. of the fluid has been evaporated and the reaction as 

 determined by test paper in the distillation tube is still neutral, the excess sulphuric 

 acid in the condenser is titrated back with one-quarter normal caustic soda solution 

 to which has been added cochineal tincture or Congo red as an indicator. The nitro- 

 gen is then calculated from the ammonia which has been distilled over (17 parts of 

 ammonia represent 14 parts of nitrogen). (For further details see Beythien, Hart- 

 wich and Klimmer). 



Fig. 1. Determination of nitrogen by Kjedahl's method, a, Combustion 



ks. b, exsiccator. 



The weight of nitrogen thus obtained is multiplied by 6.25 to obtain the weight 

 of crude protein (6.25 parts protein contain one part nitrogen by weight). 



The amount of crude protein thus indicated corresponds only approximately to 

 the albumins present, since the actual nitrogen content of albumins is not always 

 exactly 16 percent but varies between 15 and 19 percent. And again, feeding stuffs 

 contain other nitrogen compounds besides proteids (amids, alkaloids, ammonia, nitric 

 acid, etc. — (see pp. 8 and 9). Both of these sources of error, however, are small 

 in most feeding stuffs, are partly compensating, and may therefore be ignored for 

 practical purposes. In certain feeding stuffs, however, considerable quantities of 

 nitrogen-containing compounds, besides the proteins, are present, e. g., beets and the 

 leaves of cabbage, and these must be removed from the proteids before combustion. 



This is usually done according to Stutzer's method. Place 2 gm. of the finely 

 pulverized material into a breaker, add 1(X) cc. of water and heat to boiling tem- 

 perature, treat with 0.4 gm. cupric hydroxid (in case of substances rich in phosphoric 

 acid add, in addition, a few cubic centimeters of alum solution). Filter when cool, 

 wash the residue and use for the determination of nitrogen. The nitrogen thus 

 obtained indicates protein nitrogen, and the amount of pure protein may be obtained 

 by multiplying by 6.25. 



Soil, fertility and meteorological conditions exert no inconsiderable 

 influence on the protein content of feeding stuffs or forage plants. The 

 seeds of the Leguminosae, oil cakes, malt sprouts, young green forage. 



