592 DR GEORGE WILSON ON NITRIC ACID 
should not be formed in very large quantity; while ammonia forms less than 
one-10,000th of the air, perhaps much less. Nitric acid is only found in springs 
where decaying organic matter is near them, as in towns, and is formed from the 
ammonia produced in their decay, by the same process as in nitrification. Besides, 
while we have no proof that plants decompose nitric acid, which it is certainly 
possible they may do, we know that many plants, such as tobacco and sunflower, 
actually produce nitric acid, or, at least, do not destroy that which enters them.”* 
Thus far Dr Grecory. I at once concede to him that plants are largely in- 
debted to ammonia for the nitrogen found in them; and in support of the belief 
that they are also indebted to nitric acid for their nitrogen, I adduce the follow- 
ing proofs. 
Firstly, The production of nitric acid in the atmosphere during thunder- 
storms. is a certain, not a questionable fact; and the scale on which it is pro- 
duced is such as to necessitate its recognition as a portion of the azotised food of 
plants. That this should have been questioned is perhaps not strange, for the 
newly-discovered truth that ammonia is generally present in the air, could scarcely 
fail to throw into temporary oblivion the equally important truth that nitric acid 
is generally present there also. The name of the great living chemist Lirpia 
is identified with the one discovery, and the name of the great dead chemist 
CavENDIsH with the other; and we must not grudge that greater interest should 
be felt by most in the doings of the living philosopher. But assuredly it is not 
necessary to set the two truths against each other, as if they were mutually in- 
compatible, or in any respect contradictory. On the other hand, I believe that 
they are complementary, and form an essential and manifest part of that harmo- 
nious adjustment which we everywhere perceive guarding plants and animals 
against imperfect nourishment or decay. 
In the year 1781, CAvenpisu addressed himself to the task of answering this 
question, among others, “ Why does the passage of an electric spark through a 
confined portion of air, cause a diminution in its volume?”+ ‘He did not give a 
categorical reply to this question till 1785, when he published his discovery that 
a mixture of two measures of nitrogen and five measures of oxygen can be entirely 
converted into nitric acid, by sending a succession of electric sparks through it.} 
He had observed the fact, however, in 1781, in the course of the famous experi- 
ments which led to the discovery of the composition of water,—a truth to which 
I refer, because an impression is prevalent, that the conversion of a mixture of 
nitrogen and oxygen into nitric acid by the electric spark, can only be effected 
with great difficulty, whereas the undesired and unintended production of this 
acid, in trials instituted with a totally different object in view, was the chief 
* Grecory’s Organic Chemistry, Third Edition, p. 466. 
t Phil. Trans., 1784, p. 119. { Ibid, 1785, p. 372. 

