
AS A SOURCE OF THE NITROGEN FOUND IN PLANTS. 595 
of nitric acid does; yet, as in the numbers I have quoted, the weight of acid 
exceeds that of alkali three and a-half times, it appears that, so far as we have 
quantitative observations on the matter to refer to, a larger amount of nitrogen is 
offered to plants in rain-water, in the form of nitric acid, than in that of ammonia. 
I have separated the question of the occurrence of nitric acid in rain-water, 
from that of its development in the atmosphere by oxidation, and by electricity ; 
because it is not certain that the whole of the nitrates found in rain-water have 
been produced by a process like that of nitrification, or by the action of lightning- 
discharges on the air. Since rain-water is found to contain common salt, lime, 
magnesia, and the like, which have been raised into the atmosphere from the 
earth, or from the bodies of water at its surface, we cannot refuse to credit that 
nitre may be elevated in the same way. I might go further, for attention has long 
been directed to the fact, that there isa marked loss during the evaporation of 
solutions of common nitre, in consequence of that salt, although not volatile in 
the dry state, undergoing volatilisation along with the vapour of water. This 
is a secondary point, but it is important, as shewing that, apart altogether from 
oxidation, and from thunder-storms, there is a source from which the atmosphere 
everywhere may receive compounds of nitric acid. 
Fourthly, Tt has been known for more than a century, that many springs 
contain nitrates. 
Fifthly, Tt is now universally admitted, that wherever nitrogenous vegetable 
or animal matter is exposed to the air along with alkaline bases, ammonia is 
developed, and then oxidised into nitric acid, which combines with the bases. 
Now, those conditions are extensively realised all over the globe, both in culti- 
vated and uncultivated tracts of land; and in the warmer regions of the earth, 
where decomposition proceeds with greatest rapidity, the production of nitre in 
the soil is constant and immense. India alone furnishes Great Britain with all 
the nitre needed for her gunpowder. 
Siathly, The most marked nitrous districts of India are celebrated for their 
fertility, provided a due supply of water is furnished to them. 
Seventhly, The alkaline nitrates dissolved in water, and not employed in too 
strong solutions, have been found greatly to quicken the growth of plants; and the 
nitrate of soda which, from its cheapness, is the most accessible, is daily coming 
into greater use among our farmers. In the current number of the Journal of the 
Royal Agricultural Society,* will be found the last of a series of papers on this sub- 
ject, in which the virtues of nitrate of soda in increasing the amount of wheat 
yielded by a field manured with it, are placed by Mr Pusry above those of ammonia. 
It has been asserted, indeed, that alkaline nitrates are serviceable to plants 
only by furnishing them with alkalies; but I know not by what arguments it is 
proposed to defend this opinion. It is at variance with the experience of farmers, 
who find nitrate of soda, as Mr Pusry reports,} a powerful fertiliser where common 
* Vol. xiii, Part ii, p. 366. + Ibid. p. 349. 
VOL. XX. PART IV. 7¥ 
