16 SCIENTIFIC FEEDING OF ANIMALS 



burnt, and the ash which is left is ignited until it 

 becomes white. When prepared in this way the 

 ash generally contains small particles of unburnt 

 carbon. If there is much lime or potash in the food 

 the ash may contain carbon dioxide as well, and 

 in many cases this has combined so firmly with the 

 constituents of the ash that it cannot be driven off 

 by ignition. For this reason it is usual to call the 

 residue left, after ignition of a sample of a feeding- 

 stuff, " the crude ash." For most purposes a 

 determination of the crude ash suffices, but if more 

 exact figures are required, the carbon and carbon 

 dioxide have to be specially estimated, and the 

 amount of these deducted from the crude ash, leav- 

 ing what is termed the " pure ash." 



If from the total dry matter of any food which 

 has been analysed the ash is deducted, then the 

 quantity of organic substance present is obtained. 

 This " organic matter " consists of all the com- 

 bustible portion of the food — crude protein, crude 

 fat, nitrogen-free extract. 



The ash from vegetable food-stuffs contains 

 mineral matter, the most common substances pre- 

 sent being potash, soda, lime, magnesia, compounds 

 of iron and manganese, alumina, phosphoric acid, 

 silica, chlorine, all of which have been taken up 

 by the roots from the soil. In addition to these 

 there are small particles of other incombustible 

 substances, such as sand, earth, dust, etc., which 



