THE COMPOSITION OF FEEDING STUFFS 



17 



6. Fat. The residue from the preceding determination is extracted 

 with anhydrous sulfuric ether in a suitable apparatus for a considerable 

 period of time, generally 16 hours, till the fat has been completely dissolved. 

 The ether is distilled off and the residue dried at 100 C. and weighed. 

 As previously stated, the ether extract, in the case of roughage and some 

 other feeds, contains considerable impurities, as chlorophyl, wax, and 

 resins. 



c. Protein is obtained by multiplying the total nitrogen by 6.25 (see 

 p. 9), the nitrogen being determined by the Kjeldahl method, so called 

 after the inventor, a Danish chemist. In this ^method a small portion of 

 the feed (generally 1 gram) is heated with 20 c.c. sulfuric acid till the 

 organic matter has been completely decomposed and the nitrogen has been 

 changed into ammonium sulfate. This is dissolved in distilled water, 



FIG. 5. View of a chemical laboratory for analysis of feeding stuffs and other agricultural 

 products. (Wisconsin Station.) 



and 50 c.c. of a concentrated soda solution are added, the flask being 

 connected with a distillation apparatus and heat applied. A certain 

 quantity of standard hydrochloric acid solution, more than sufficient to 

 neutralize the ammonia obtained in the oxidation of the protein, has been 

 previously added in the receiving flask, and the distillation is now con- 

 tinued till all ammonia has been distilled over. The excess of acid in the 

 receiving flask is then accurately titrated back (neutralized), and from the 

 volume of acid used the amount of nitrogen in the sample is obtained. 

 This is calculated in percentage of the amount of sample weighed out, 

 and by multiplying by 6.25 the percentage of protein contained in the 

 sample is obtained. 



d. Fiber is determined in the residue from the fat extraction by boiling 

 first with 200 c.c. of a 1.25 per cent sulfuric acid solution and then with 

 200 c.c. of a soda solution of the same strength. After filtering, drying, and 

 weighing, the residue is ignited, and the loss in weight, calculated on the 

 amount of the sample originally weighed out, shows the percentage of 



