DOES NOT YIELD NITROGEN TO PLANTS. 221 



acid in rain-water would be appreciably greater. But the known 

 examinations of the spring and river waters of those regions ; 

 for example, of the waters of Paipa, near Tunga, of the water of 

 the Rio Vinagre. and of the hot mineral springs of the Cordilleras, 

 the analyses of which were instituted by Boussingault, in South 

 America, without the presence of nitrates being detected, show 

 that there is no foundation for the opinion that a sensibly greater 

 quantity of nitric acid is generated in those regions, by the action 

 of lightning, than in the temperate zones. 



It follows, from the preceding observations, that nitric acid, or 

 its salts, are not destined by nature to yield nitrogen to plants. 

 If it were actually the case that nitric acid did yield to plants 

 their nitrogen, we must assume that this source was accessible to 

 all plants without distinction. But it is completely excluded 

 from marine plants ; and even in the case of the terrestrial plants 

 of the temperate and cold zones, the rare occurrence of thunder- 

 storms would prevent us from considering that any appreciable 

 quantity of their nitrogen could arise from nitric acid generated 

 by the action of lightning on the constituents of air. 



Butj even on the assumption that nitric acid does take a de- 

 cided part in vegetable life, ammonia still remains as the ultioiate 

 source of the nitrogen of plants ; for, as far as oar knowledge 

 at present extends, all the nitric acid on the surface of the earth 

 is formed by the eremacausis of ammonia, and it is not impro- 

 bable that the nitric acid, which occurs in the rain of thunder- 

 storms, may be dependent on the presence of the same body. 



Although we thus trace back the action of all animal and 

 other substances containing nitrogen, to the only compound which 

 furnishes this element to all plants, in a state of nature, we do 

 not of course mean to exclude the application of these other 

 matters to the purposes of agriculture. When we know that 

 woollen rags, horn, and hair, in the progress of decay, offer a 

 slow but continued supply of ammonia, it follows, that we may 

 use them wherever their price, in comparison with the advantage 

 anticipated, does not exclude their application. 



The same reasoning holds good in the case of nitrates. In 

 these, nitrogen exists in another form than that of ammonia. 

 Nitric acid, or rather nitrous acid, is, in its chemical relations, 



