4 SCIENTIFIC FEEDING OF ANIMALS 



(i) Water. 



That portion of a food which disappears on 

 drying is called the water, or moisture. If the 

 percentage of water in a food-stuff, such as grass 

 or hay, had to be determined, it would not be suffi- 

 cient to dry a sample at ordinary temperatures in 

 the air, for in this way the whole of the water would 

 not be driven off. A portion would still remain, 

 varying from 11-20% of the total weight, and the 

 sample would only be " air dried." Water can only 

 be completely driven off by drying the finely ground 

 sample of food for a considerable time at ioo° C. 

 Usually this is continued until the weight of the 

 substance remains constant, and this is the method 

 adopted when an exact chemical analysis is being 

 made. Many feeding-stuffs, particularly those that 

 have been acted upon by bacteria or moulds, 

 e.g. silage, as well as the plants and seeds contain- 

 ing ethereal oils, lose some other substances in 

 addition to water when heated at ioo°. These 

 volatile materials, such as acetic acid, lactic acid, 

 butyric acid, some ethereal oils, ammonia, etc., 

 necessitate special precautions being taken when 

 the water has to be estimated in a food in which 

 they are present. 



That which is left after complete desiccation in 

 the manner described above is called the " dry 

 matter." 



