594 DR GEORGE WILSON ON NITRIC ACID 
this point I do not dwell; for I am content with the alternative conclusion, that 
the nitric acid of thunder-storms either descends at once to the earth, and feeds 
the most luxuriant vegetation known to us; or that it is diffused through the en- 
tire atmosphere, and is available for the nutrition of the plants of all lands. 
Thirdly, Rain-water is often found to contain nitric acid in combination with 
different bases. The most recent observations on this point with which I am 
acquainted, are those of M. BarraL, communicated to the French Academy, and 
approved by a committee of that body. If Barrat’s results are confirmed, and 
are not found to be exceptional, they will compel us to acknowledge a much 
larger proportion of nitric acid, as normally present in the atmosphere, than is 
generally imagined. His researches were made on the water collected in the 
rain-gauges of the Observatory of Paris in 1851 and 1852. 
The following are his general conclusions :— 
* 1°. During one year, reckoning from July 1, 1851, to June 30, 1852, there 
fell at Paris a quantity of nitrogen in combination, equal to 20-04 lbs. avoirdu- 
pois to the English imperial acre; namely, 11°13 lbs. in the condition of nitric acid, 
and 8:91 lbs. in the condition of ammonia.* 
«© 2°. The quantity of ammonia which fell during that period amounted to 
12°29 lbs. to the acre. 
© 3°. The quantity of anhydrous nitric acid which fell during the same period 
amounted to 41-24 Ibs. to the acre. 
« 4°. The quantity of ammonia diminished in the months during which the 
quantity of nitric acid increased. 
«5°. The quantity of nitric acid increased whenever the weather became 
stormy. 
« 6°. During the months only of February, March, April, and June, the quantity 
of nitrogen in the form of nitric acid, was a little less than the quantity of nitrogen 
in the form of ammonia.”’}+ 
These observations apply to rain-water collected in the neighbourhood of a 
ereat city, and do not admit of direct comparison with the purer rain-water of 
the open country; but they are very remarkable, not merely as shewing that 
rain brings down nitric acid as well as ammonia, but that, in certain places at 
least, it contains more nitric acid than ammonia. And although a given weight 
of ammonia contains three times the amount of nitrogen which the same weight 
* There is some mistake in Barrat’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 Ibs. These, ac- 
cordingly, are the numbers which should appear in the first paragraph of Barrat’s conclusions. 
+ Comptes Rendus pour 27 Septembre 1852, p. 431. 
