FORMATION OF NITRE. 2i1 



port of vegetation, and without the presence of which nitric acid 

 could not be formed. 



The presence of alkaline nitrates in a soil indicates with the 

 greatest certainty, that the most important conditions for the 

 growth of plants are united in it ; but these salts are not the pri- 

 mary causes of the growth, because both the formation of nitre, 

 and the luxuriant growth of plants, are effects of similar causes 

 acting on the earth. It is certain that the vicinity of the saltpetre 

 mines of Quarta Jaga and Santa Rosa, described by Darwin, 

 although saturated with nitrates, forms a complete waste, in which 

 a small cactus is scarcely able to grow. The cause of its sterility 

 may be the want of rain ; but if it were moist, and obtained 

 abundant supplies of rain, the nitrates would have disappeared 

 long since ; and, even without their presence, vegetation would 

 flourish luxuriantly in this climate. 



The common error is to confound a soil, in which nitrates 

 exist, with one in which they are in the act of forming. If the 

 first soil be Wanting in the conditions (animal matter) necessary 

 for a further formation of nitric acid, it will prove sterile, but 

 will, on the contrary, be fertile if these conditions exist. The 

 latter, and not the nitrates, are therefore the causes of the better 

 growth of vegetation. 



It follows from the preceding observations, that, as far as our 

 experiments extend, the formation of nitric acid on the surface of 

 the earth, is dependent on the presence of animal matter. 



But as animal substances receive their nitrogen from the 

 atmosphere in the form of ammonia, the primary origin of the 

 nitric acid of nitrates must be the ammonia of the atmosphere. 

 But it may be affirmed, in addition to this, that ammonia is not 

 the only ultimate source of, but that it is actually the immediate 

 source of nitric acid. We have reason to believe that the nitro- 

 gen of decaying animal substances assumes the form of ammonia, 

 before being converted into nitric acid ; and that it must first be 

 in the state of ammonia, before it is able to form nitric acid with 

 the oxygen of the air.* Hence we must view ammonia as the 

 principal source of the formation of nitric acid on the surface of 



• See the Chapter on Erpmacausi* in sennd part of thi9 book. 

 11 



