312 VEGETABLE MANURES. 



cidedly objectionable; it increases the rapidity of 

 decomposition, and tends to the formation of a por- 

 tion of nitric acid, but its use causes the loss of a 

 large quantity of ammonia, in consequence of its 

 power of decomposing all the salts of ammonia (152), 

 combining with the acid which they contain, and 

 expelling the ammonia in the state of gas. The 

 addition of lime renders putrefaction a far less 

 noisome process, as the lime absorbs the sulphuretted 

 hydrogen evolved (182), which would otherwise 

 escape into the air. 



838. "Wood ashes mixed with putrefying animal 

 matters act in a similar manner to lime ; the alkali 

 which they generally contain frequently accelerates 

 decomposition, but occasions loss of ammonia. 



839. A good deal of what has been said respecting 

 animal manures is equally applicable to those of 

 vegetable origin ; but in general the decay of vege- 

 table manures is far less rapid than that of animal 

 substances, and they are more valuable for their 

 mechanical effects, and the carbonic acid and saline 

 matters which they supply ; whilst, in addition to 

 these, animal manures yield ammonia, the substance 

 of which is indispensable to the formation of gluten, 

 albumen, fibrin, and caseine, the most important of 

 the constituents of vegetables (602). 



840. The use of decaying vegetable matters has 

 already been described whilst speaking of the nature 

 of humus, and the organic constituents of the soil 



