126 ACTION OF SALTS. 



in geine, and nitrogen in its ammonia compounds. Gelne 

 thus contains the elements of water, ammonia, and carbonic 

 acid, or the whole organic food of plants. The nitrogen, 

 also, exists in the air. It forms 80 per cent, of it. In this 

 state it cannot be assimilated by the plant till that has put 

 forth its leaves. Its only source for the roots and for the 

 germinating seed, is that arising, either from the geine, or 

 from ammonia evolved by the fermenting dung, or from 

 nitrates. In either case, whether the nitrogen arises from 

 the geine or from the nitrates, decomposition takes place by 

 the action of the living plant. 



168. Under this view, nitre is found to be one of the most 

 active, bland, and beneficial salts. Nitre consists of an 

 alkali, and an acid composed of one part of nitrogen to five 

 of oxygen. The plant decomposes these. The disposition 

 of the alkali, or of the base, has been already considered. 

 What becomes of its acid 1 That, too, is slowly decomposed. 

 What becomes of its elements ? The one part of nitrogen 

 is taken up by the living plant, or it may, under the com- 

 bined influences to which it is now subjected, be in part re- 

 converted into ammonia, by the hydrogen of the geine, and 

 so act on that as alkali. What becomes of its five parts of 

 oxygen ? The answer is full of the highest interest. It is a 

 key, unlocking the chambers of mystery. The oxygen acts, 

 first, on the geine of the soil, and secondly, on the sili- 

 cates. And first, on geine ; let it be supposed that this is 

 wholly insoluble, perfectly inert. It has been already said 

 that air converts this into soluble geine. This action de- 

 pends on the oxygen of the air acting on the carbon, by 

 which carbonic acid is formed ; the geine is thus rendered 

 soluble, while the carbonic acid escaping, acts on the sili- 

 cates of the soil, and these are thus decomposed. There is 

 no mystery now in the action of saltpetre, or nitrates of 



