596 DR GEORGE WILSON ON NITRIC ACID 
salt is of no avail. But it is needless to enlarge upon this, for even if it were con- 
ceded that soda is the more important constituent of nitrate of soda, considered 
as a fertiliser, it is manifest that it must make a difference to a plant whether 
soda be supplied to it combined with carbonic, hydrochloric, sulphuric, or nitric 
acid ; and that in the case of nitrate of soda, the plant must in some way dispose 
of the nitric acid before it can avail itself of the soda; so that the question must 
be answered, What becomes of the nitric acid which enters plants ? 
To this, one reply is offered in the quotation which I commenced by reading. 
The presence of nitrates in tobacco, sunflower, and certain other plants, is thought 
to shew that if they do not even possess the power of producing nitric acid, they 
at least cannot decompose it. But surely this is proving too much. For if the 
presence of undecomposed nitric acid in a plant shews that it cannot decompose 
that acid, then the presence of ammonia shews that it cannot decompose ammonia, 
and the presence of undecomposed sulphuric acid shews that it cannot decompose 
this acid; and for the same reason, as plants all contain undecomposed chlorides, 
carbonates, water, and carbonic acid, it should be held that they can decompose 
none of these. In short, it should be contended that a plant can decompose no- 
thing, and that its existence is a chemical contradiction. If we refuse to draw this 
conclusion in the case of the other oxides and acids which are found in plants, 
we must extend our refusal to nitric acid, which is cireumstanced exactly as the 
others are. 
As for the opinion that plants may produce nitric acid, it is quite possible 
that they can, although for reasons to be presently mentioned it does not seem 
likely that they generally do; but it would be unwise to speak confidently on the 
matter. The only conclusion certainly deducible from the presence of nitrates in 
plants is, that at least nitric acid does not act injuriously on them. 
Thus far, then, it has been I think satisfactorily shewn— 
Firstly, That nitrates are largely offered to plants, both as they grow wild 
and as they are artificially cultivated. 
Secondly, That plants do not refuse the nitrates thus offered them. 
Thirdly, That the nitrates which enter plants do not, if properly diluted, do 
injury to any class of them; whilst, 
Fourthly, They largely promote the growth of many of the most important 
among them. 
It remains to inquire, Can plants decompose nitric acid, and avail themselves 
of its nitrogen? I can offer no direct or demonstrative proof that plants possess 
the power of effecting this decomposition. Direct proof is not to be had in the 
matter, but the following powerful considerations may be urged in support of the 
belief that plants can decompose nitric acid. 
From the moment of the discovery that water is the oxide of hydrogen, 
chemists perceived that the great characteristic function of a living plant, con- 
sidered as a piece of chemical apparatus, was to deprive oxides of their oxygen, 
