472 
The Atmosphere Considered 
[Odlober, 
salts, and in rain from thunder-showers the ammonia is 
combined as nitrate, the effedt of the electric discharge 
being to oxidise a portion of the nitrogen of the air to nitric 
acid.* 
The atmospheric ammonia is not without its effedt on 
vegetation. It is certain that plants grown in air perfectly 
free from ammonia never flourish to the same extent as 
those surrounded by an atmosphere containing some of it ; 
and the experiments of Boussingault, Lawes, and Gilbert — 
borne out as they are by those of Stockhart, Peters, and 
Sachs, and lately by the very conclusive researches of 
Schloesingf and A. MayerJ — show that at least a consider- 
able part of, if not all, the nitrogen of plants is derived 
from this source. Now the geological connection of this is 
at once plain, for the decomposition of nitrogenous matter 
such as plants, in rocks, may lead partly to the formation 
of nitrates, or, by the evolution of nitrogen and ammonia in 
volcanic regions, give rise to other minerals, as I shall show 
presently. 
Occasionally the ammonia is absorbed direCtly from the 
air by surface mineral matter, as in the case of the volcanic 
earth of the Solfatara of Puzzuoli. S. de Luca|| tells us that 
this contains a quantity of sulphur and arsenic which under 
the influence of air and moisture form acids, and at once, 
combine with the atmospheric ammonia. But it is to the 
decay of vegetation that the vast majority of the nitrogen 
compounds which are met with, either as minerals or as 
volcanic emanations, are due, and in whatever state the 
nitrogen was originally absorbed — whether in the free state 
or as ammonia — it cannot be doubted that all the nitrogen 
compounds contained in the earth, as it now exists, are 
traceable entirely to past and present atmospheres. 
The nitrogenous compounds so obtained are themselves 
subjecT to an endless variety of changes, in which the gases 
already described bear no unimportant parts — reducing and 
oxidising ; and these changes, or the effect of heat, may 
* Liebig found that of seventy-seven specimens of rain-water, seventeen, 
collected during thunder-storms, contained nitric acid combined with lime and 
ammonia. Of the remaining sixty but two contained traces of it. — Bischof, 
op. cit., i., p. 214. According to Bottger, the induCtion-spark passed through 
moist air gives nitrogen peroxide and ozone, but in dry air gives nitrous fumes. 
— Cluin. Centr. (1873), 497. Doubtless similar results follow discharges of 
natural electricity. 
f Comptes Rendus, lxxviii., 1700. 
X Deut. Chem. Ges. Ber., vi., 1404— -1413, and Landw. Versuchs. Stat., 
xvii., 329. „ . 
j| Comptes Rendus, Ixxx., 674. 
