THE FEEDING OF ANIMALS 1G5 



By moisture is meant the loss which the food-stuflf undergoes 

 when heated in a steam-bath until constant. This may be 

 taken without much error to be water, though other volatile 

 constituents of the material may be lost. An error in the 

 opposite direction may be introduced by the oxidation of some 

 constituent, unless the heating is done, as it sometimes is, in a 

 current of hydrogen or of nitrogen. Certain oils — e.g.^ lin- 

 seed — absorb a considerable quantity of oxygen when heated, 

 in air. 



Ash is the amount left by heating the material to redness in 

 air until all black portions of carbon have disappeared. The 

 residue obtained does not necessarily contain the true mineral 

 constituents of the food-stufi" in the same form as they were 

 actually present. Indeed, it almost invariably happens that 

 the various constituents are left in an entirely different state; 

 e.g.^ potassium and calcium are left in the ash largely as 

 carbonates, though in the plant they are doubtless present as 

 organic salts (malates or oxalates). The sulphates in the ash, 

 too, are often derived from sulphur existing as albuminoids. 



Crude fibre is determined by the somewhat arbitrary method 

 of boiling a weighed portion of the material successively with 

 dilute sulphuric acid and a solution of caustic soda. The 

 organic matter which resists this treatment is reported as crude 

 fibre. It consists generally of woody matter, but it is quite 

 empiric to assume, as is sometimes done, that it is a measure 

 of the material which would resist digestion if fed to an 

 animal. 



N-free Extract, or Soluble Carbohydrates. — This is always 

 determined by difierence — by subtracting the sum of all the 

 other constituents from 100. The result, which includes the . 

 accumulated errors of all the other items, is assumed to consist 

 of starch, sugar, and other carboh^^^drates. This is not very 



