PRACTICAL AGRICULTURE. 43 



the inoisture it contains, without permitting: the escape 

 of its ammonia, it may be put into such a form as will 

 allow it 1 be transported even to great dih>tances. This 

 is already attempted in many places ; and tiie prepara- 

 tion of human excrements for exportation constitutes 

 not an unimportant branch of industry. But the man- 

 ner in which this is done, is not always the most ju- 

 dicious. 



It is quite certain that the vegetable constituents of 

 the excrements with which we manure our fields, can- 

 not be entirely without influence upon the growth of 

 the crops on them ; for they will decay, and thus furnish 

 carbonic acid to the young plants. But it cannot be 

 imagined that their influence is very great, when it is 

 considered that a good soil is manured only once every 

 six or seven years; that the quantity of carbon thus 

 given to the land corresponds only to 5 per cent, of what 

 is removed in the form of herbs, straw, or grain ; and 

 further, that the rain-water received by a soil contains 

 much more carbon in the form of carbonic acid than 

 these vegetable constituents of animal excrement. 



The peculiar action, then, of solid, as opposed to fluid, 

 animal excrements, is limited to their inorganic consti- 

 tuents, rather than to the presence of the partially 

 changed vegetable or organized matter which they con- 

 tain. Horse-dung contains a large portion of such par- 

 tially altered vegetable matter; and the reason why 

 night-soil is a more powerful manure, is that, relatively, 

 it contains less vegetable matter, while nitrogen is more 

 abundant ; and this, principally, because its weight is 

 materially made up by the liquid excrement, or urine, 

 always forming part of its composition. The restoration 

 of inorganic matter to the land, is the chief value arising 

 from the application of the dung of cattle. A certain 

 amount of inorganic matter is removed with every crop. 

 If we manure that land with the dung of the cow or 

 sheep, we restore to the surface silicate of potash, and 

 some salts of phosphoric acid. If we use horse-dung, 

 we supply, chiefly, phosphate of magnesia and silicate 

 of potash. In the straw which has served as litter, we 



