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 100 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 100. 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." 



