The Atmosphei'e as a source of Niti'ogen to Plants. 255 
or less than half that found by Giager, and one twentieth of 
that of Kemp. 
M. Isidore Pierre, another Continental chemist, in two analyses 
of this kind, found in a million parts of air taken at about 12 
feet and 25 feet from the ground respectively 3^ and h part of 
ammonia. 
It is obvious, however, that the discrepancies between these 
different experimenters are too great to allow us to draw from their 
results any conclusion which could be employed in elucidation of 
questions of agricultural philosophy, or in improvements of agri- 
cultural practice — tliat they proceed either from defects in the 
methods of examination, or tliat they indicate very great varia- 
tions in the composition of the air at different times and under 
different circumstances is also plain. Perhaps both of these ex- 
planations may be in part correct. 
VVe liave briefly alluded to these earlier attempts to ascertain 
the (quantity of ammonia in the air, in order that a tolerably 
correct history of the subject might be given. It is, however, 
within the last five or six years that the chief contributions to 
this branch of knowledge have been made, and it is requisite 
that we should treat somewhat more in detail the experiments 
which have been carried out, partly to determine the source of 
nitrogen in plants, and partly to ascertain in reference to the 
same question the proportion of ammonia and nitric acid in 
air, and in rain-water. Associated with the former subject we 
have the names of MM. Ville and Boussingault in France, and 
with the latter those of MM. Ville, Boussingault, and Barral in 
France, and of Mr, Lawes and Dr. Gilbert in this country. 
I shall take them in succession, commencing with the experi- 
ments of M. Ville. The first series of experiments made by M. 
Ville relates to the proportion of ammonia in the air. They 
were commenced in the month of June, 1849, and extended 
over the remainder of that year and the whole of the year 1850. 
A second series made in 1852 comprised the first six months in 
that year. M. Ville's researches are marked by a most scrupu- 
lous attention to every circumstance which would conduce to a 
correct result. Fully alive to the sources of error which had 
compromised the experiments of those who preceded him, he 
seems to have anticipated and provided against the objections 
which might be raised against his own. 
One great fault of previous attempts to determine the ammonia 
in the air, was the small quantity of the latter that was operated 
upon. At the most the proportion of ammonia is remarkably 
small, and it is easy to understand how in operating upon a small 
bulk of air the errors introduced in one form or another should 
exceed the total quantity of ammonia actually present. 
