140 MANURE. 



the presence of animal matter ; under the influence of porous 

 materials, aided by alkalies, or lime, the elements of air 

 combine and form nitric acid and nitrates, when bases are 

 present. This action is greatly assisted by ammonia, which 

 acts by catalysis. The great use of the animal matter is to 

 produce this al]*[ali, or ammonia. If no alkaline base is 

 present, it becomes the source of the formation of nitrate of 

 ammonia. This salt being decomposed by the living plant, 

 its nitric acid acts on the silicates, and saltpetre or nitrate of 

 potash is produced. The agency of this, as a manure, has 

 already been considered (167, 168). The action, also, of 

 other salts in dung, will be easily understood by reference 

 to the fifth chapter. 



195. There is still a powerful effect due to the geine, or 

 to the hay in its conversion to that state. During this pro- 

 cess, a great quantity of carbonic acid is liberated. The 

 decomposing action of this upon silicates of the soil, and the 

 consequent liberation of their alkali, has also been explained 

 (133). All these actions are to be remembered, in account- 

 ing for the action of cow-dung. The geine, salts, nitrogen, 

 each acts ; the geine has an action, the salts an action, the 

 nitrogen an action. They all contribute to one end. Three 

 substances, but one result, viz., vegetation. 



196. The nitrogen, then, in dung, is that organic element 

 to which must be attributed its chief enriching quality. The 

 nitrogen is the basis, both of the production of ammonia, 

 and of the formation of nitrates. Hence, the quantity of 

 nitrogen in manures will form a very good element for the 

 estimation of their value. Manures will be found rich, in 

 proportion to their quantity of nitrogen, or their power of 

 forming nitrates. This is the great and first cause of the 

 enriching power of dung. Though the action of all excre- 

 ments has been referred to their inorganic parts only, com- 



