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XLI—On Nitric Acid as a Source of the Nitrogen found in Plants. 
By Grorce Witson, M.D. 
(Read 4th April 1853.) 
The source from which plants obtain nitrogen, which is now recognised as one 
of their most important elements, has, from the first recognition of its importance, 
been matter of dispute. Latterly, however, chemists and physiologists have 
pretty unanimously come to the conclusion, that a large (perhaps the largest) 
part of the nitrogen of vegetables is derived from ammonia; whilst much discus- 
sion has been carried on as to the question, Is any part of their nitrogen yielded 
by nitric acid? 
The most able advocate in this country of the claims of ammonia is Dr Gre- 
cory. The most able advocate of the claims of nitric acid is Professor Jounston 
of Durham, and the opposite conclusions to which accomplished chemists like 
these have come in reference to the point in dispute, have perplexed botanists, who 
know not which view to prefer. The extent to which they are pressed by this 
dilemma, has been so strongly represented to me by Dr Batrour, that I have 
engaged to bring the subject, as I now do, before this Society. I shall sedulously 
avoid discussing the question in a polemical spirit; and, as the shortest and most 
satisfactory way of doing justice to the rival views, I shall select Dr Grecory’s 
clear and concise statement, as representing the opinions of those who deny that 
nitric acid is part of the food of plants; and then proceed to state what appear to 
me conclusive proofs that nitric acid does supply plants with nitrogen. 
Dr Grecory writes thus:—‘ Let us now attend to the nitrogen of plants. 
This, as already stated, is supplied to wild plants entirely by the air, and, so far 
as we know, only in the form of ammonia. Some authors have held that nitric 
acid furnishes nitrogen to plants, and that this acid is formed in the air by 
thunder-storms, and carried down by the rain. And they point to the occur- 
rence of nitric acid in springs in proof of this. Now it is true that nitric acid 
is formed in thunder-storms, but in very minute quantity, whereas ammonia is, 
and must be, present in the air at all times. Indeed there is reason to believe 
that the nitric acid of storms is produced by the oxidation of the ammonia of 
the air, as in nitrification, where ammonia is oxidised into nitric acid and water 
NH,+0,=NO,,3 HO; so that even if nitric acid did yield nitrogen to plants, 
that nitrogen would be derived from ammonia. This would account, too, for the 
small amount of nitric acid formed. For if it were produced-by the action of elec- 
tricity on the nitrogen and oxygen of the air, there seems to be no reason why it 
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