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Published online by Cambridge University Press: 17 January 2013
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 discussion 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 Gregory. The most able advocate of the claims of nitric acid is Professor Johnston 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 Balfour, 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 Gregory'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.
page 592 note * Gregory's Organic Chemistry. Third Edition, p. 466.
page 592 note † Phil. Trans., 1784, p. 119.
page 592 note ‡ Ibid, 1785, p. 372.
page 593 note * Phil. Trans., 1788, p. 261.
page 593 note * Electrical Researches, vol. i., pp. 90, 91.
page 594 note * There is some mistake in Barral's numbers, for the statements in the first paragraph do not agree with those in the second and third; as the numbers, however, for nitrogen are calculated from the observed quantities of nitric acid and ammonia, the figures representing these are assumed as the correct ones.
If so, the quantity of “nitrogen in combination” is equal to 20·81 lbs. per acre; that of the nitrogen in nitric acid is 10·69 lbs.; and that of the nitrogen in ammonia, 10·12 lbs. These, accordingly, are the numbers which should appear in the first paragraph of Barral's conclusions.
page 594 note † Comptes Rendus pour 27 Septembre 1852, p. 431.
page 595 note * Vol. xiii., Part ii., p. 366.
page 595 note † Ibid. p. 349.