24 



THE FEEDING OF ANIMALS 



that part of the ignited or decayed substance which dis- 

 appears in the air as gases, and the latter the residue 

 or ash. 



29. Combustion does not destroy matter. It should 

 be well understood that combustion does not involve 

 a loss of matter; only a change into other forms. If we 

 were to collect the gases which pass off from a stick of 

 wood that is burned, consisting mostly of carbon dioxid, 

 vapor of water, and certain compounds of nitrogen, we 

 would find that their total weight, plus that of the ash 

 residue, is even greater than that of the dry wood, because 

 the carbon and the hydrogen of the wood have united 

 during the combustion with an increased amount of 

 oxygen. The carbon, oxygen, hydrogen, and nitrogen of 

 the plant or animal tissue belong to the combustible 

 portion, although small amounts of two of these elements 

 are found in the ash, as it is usually estimated. The 

 remainder of the fifteen elements previously named is 

 supposed to appear wholly in the ash, although in different 

 combinations from what they exist in the plant. 



30. Relation of combustible to incombustible por- 

 tions. The relation in quantity of the combustible and 

 incombustible parts of vegetable and animal dry matter 

 is illustrated below: 



TABLE V 



