ACTION OF SALTS. 117 



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

 the most active of salts ; yet bland and beneficial in 

 all its actions. Nitre is alkali, and 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 be- 

 comes of its acid ? That too, slowly is decomposed. 

 What becomes of its elements ? The one part of 

 nitrogen is taken up by the living plant, or it may, 

 under the combined influences to which it is now sub- 

 jected, be in part reconverted, into ammonia by the 

 hydrogen of the geine, and so act on that, as alkali. 

 What becomes of its five parts of oxygen ? The an- 

 swer is full of the highest interest. It is a master's 

 key, unlocking the chambers of mystery. The oxy- 

 gen acts, first on the geine of the soil, and secondly 

 on the silicates. And first on geine; let it be sup- 

 posed that this is wholly insoluble, perfectly inert. 

 It has been already said, that air converts this into 

 soluble geine. This action depends 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 silicates 

 of the soil, and these are thus decomposed. There 

 is no mystery now in the action of saltpetre or ni- 

 trates of alkalies. The immediate effects are due, to 



