118 LESSONS IN CHEMISTRY. 



9. 10 lbs. of its weight, and afforded only one pound of that 

 substance which it is so important to economise. 



170. The dung of the pig usually contains about 75 per 

 cent of water, and is generally regarded as affording a colder 

 manure than that of the horse or cow; but as the pig is a 

 general feeder, the manure which it yields will frequently be 

 rich in nitrogen. On the continent it is much employed in the 

 cultivation of hemp, but is supposed to give a disagreeable 

 flavour when appHed to the root-crops. 



171. The dung of the sheep is of great importance as a 

 manure in many districts, both in England and this country. 

 In Wiltshire, the usual method of applying it is by folding 

 the sheep on the bare fallow, and shifting the hurdles every 

 night so as to distribute the manure over the field. On the 

 light soils of Norfolk also, it has been found of great advan- 

 tage to allow the sheep to consume the crops in the field, by 

 which means the manure is trodden in, and its rapid fermenta- 

 tion prevented, and the ground at the same time consolidated. 

 In the quantity of nitrogen which it contams, and conse- 

 quently in its tendency to ferment, sheep-dung may be 

 regarded as intermediate between that of the cow and horse. 

 All these manures contain the ingredients which plants 

 remove from our fields, and by their careful restoration to 

 the soil you will supply your crops with the materials which 

 they require, in the form best adapted for their nomishment. 

 Experience has taught farmers how much the value of the 

 manure which is produced by an animal, is influenced by the 

 food with which it is supplied ; and that a cow fed upon highly 

 nutritious substances, such as bean-meal and oil-cake (77), 

 yields a manure containing a larger amount of fertiHzing 

 matter than one fed upon straw and turnips. 



172. It has also been found that the quality of the dung 

 of an animal depends upon its age and the purpose for 



t which it is kept. Thus, the dung of growing animals is not 

 jso rich in fertilizing materials as that of full-grown cattle. 

 ^ To enable you to understand how this is, it will be useful 

 briefly to describe the changes which food is made to undergo 

 when taken into the body. You will recollect that I stated 

 to you in a preceding chapter (79), that the great bulk of 

 every plant cultivated for food consisted of certain compounds 

 '] produced by the union of the four simple elementary bodies, 

 / oxygen, hydrogen, nitrogen, and carbon ; and that while one 



