COMPOSITION OF ANIMALS AND OF FEEDING STUFFS 67 



necessary to be content in most cases with a separation of the 

 plant substances into a few major groups or sub-groups of in- 

 gredients. As ordinarily carried out, feeding stuffs analysis 

 recognizes seven of these categories, viz., water, ash, protein, 

 non-protein, ether extract, crude fiber and nitrogen-free ex- 

 tract. 



101. Water. The amount of water in a feeding stuff is 

 commonly inferred from the loss of weight which the substance 

 undergoes at a temperature above the boiling point of water. 

 There is also a possibility, however, of a loss of other volatile 

 matter besides water, while, on the other hand, some substances 

 tend to absorb oxygen and thus increase in weight, especially 

 when dried in air at a high temperature. The exact deter- 

 mination of water and dry matter, therefore, is by no means an 

 easy problem, but the results obtained by the ordinary methods 

 are sufficiently exact for almost all purposes related to stock 

 feeding. Commonly, the residue is weighed and regarded as 

 dry matter, the amount of water being obtained by difference. 



102. Ash. In the ordinary feeding stuffs analysis, ash is 

 equivalent to the residue left after complete incineration of the 

 substance in air or oxygen, the process being carried out at as 

 low a temperature as practicable in order to avoid volatilization 

 of part of the alkalies present. 



That this method fails entirely to distinguish between those ele- 

 ments which were originally present as electrolytes and those which 

 were in organic combination has already been pointed out (5) , as has 

 also the fact that certain elements, notably sulphur and phosphorus, 

 are only partially recovered in the ash by the ordinary method of 

 preparation. As the study of the functions of the ash ingredients pro- 

 gresses, it may be anticipated that we shall come to determine the 

 several elements involved in the way most appropriate to each rather 

 than simply to determine the ash as a whole. 



103. Nitrogenous constituents. As yet no methods exist 

 for the quantitative separation of the nitrogenous constituents 

 from the other ingredients of plants. While much labor has 

 been expended upon a study of the individual proteins of a com- 

 paratively few vegetable materials, and while in some instances 

 it is possible to state with approximate accuracy the amounts 

 of the several proteins present, nevertheless the only available 

 methods for the determination of the nitrogenous compounds 



