256 The Atmosphere as a source of Nitrogen to Plants. 
The experiment of Giii^er before alluded to was made on 
somewhat less than 40 cubic feet of air, those of Mr. Kemp and 
M. Fresenius on about 13 cubic feet. M. Isidore Pierre 
operated upon about 90 and 140 cubic feet respectively. The 
quantities of air upon whidi M. Ville made his experiments, 
varied from 700 to nearly 2000 cubic feet. 
M. Ville's method of determining the ammonia consisted in 
causin<r a given quantity of air to pass through liquids capable of 
lemoving and retaining it. It is unnecessary to describe the 
apparatus employed by him, and it will be sufficient to state that 
every precaution was taken to exclude dust, insects, and other 
substances which might vitiate tlie results, and that the air was 
taken from a considerable height from the ground, and at a distance 
from any source of putrid emanations. M. Ville made altogether 
IG determinations of the ammonia in the air. In the first of his 
experiments, made in the interior of Paris, but in a large garden 
more than 100 yards from any house, and with air taken from 
between 30 and 40 feet above the ground, he found the ammonia 
in 1 million parts of air to be 0"0237 parts. In his seccmd series 
of experiments, made at Grenelle, in the suburbs of Paris, the 
proportion of ammonia in 1 million parts of air was 0'0210, or 
sliglitly less than in the preceding case. It will be observed that 
this is very much less (about one-fifth) than that found by Fre- 
senius. 
I have carefully considered his statements and his method of 
examination, and I cannot see any probable source of error; on 
the contrary, such care and precision seem to have been intro- 
duced into this inquiry, that M. Ville's results would appear to 
merit every confidence. The other question, to a solution of 
which M. Ville devoted his efforts, was — Can the nitrogen of the 
air be employed in the nutrition of plants? We have before 
described the experiments made by M. Boussingault to ascertain 
whether plants could obtain nitrogen otherwise than from the 
soil, or manure. He found that they did acquire nitrogen in some 
form from the air ; but his experiments did not show whether it 
was the atmospheric nitrogen, or whether it was derived Irom the 
ammonia. M. Ville endeavoured to till up this blank in our 
knowledge of the processes of vegetation. Two methods were 
employed by him : the first was by means of an apparatus, similar 
to that used in his other experiments, to supply daily a tolerably 
large but accurately measured quantity of air to plants growing 
in glass cases ; the ammonia contained in a similar quantity of 
air was carefully ascertained at the same time. The seeds from 
which tlie plants were raised were transplanted as soon as they 
came up into calcined sand, to which a certain quantity of the 
ash of similar seeds was added : they were watered with distilled 
