444 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
nately, however, even quantitative results established by laboratory methods do not 
admit of very direct and certain application in accounting, quantitatively, for the amount 
of combined nitrogen that may be so fixed, to a given depth, over a given area of land, 
within a given time. We hope, however, to treat of this subject in some detail on some 
future occasion. 
(4 & 5) The circumstances of the formation of ammonia, or nitric acid, from gaseous, 
dissolved, or nascent Nitrogen, are at present involved in too much obscurity, and are 
the subject of too much conflicting statement for their consideration to serve us much 
in our present inquiry. The various assumed actions are, as yet, by no means all 
clearly established in a merely qualitative way; and still less, quantitatively. More- 
over, as in the case of absorption, so in that of the formation of ammonia, or of nitric 
acid, there would be considerable difficulty and uncertainty in applying the results 
of laboratory experiments to the estimation of the probable amount of the Nitrogen 
of vegetation due to such sources. To some of the questions involved, we shall, how- 
ever, have to refer more or less in detail in discussing the conditions of the experiments 
which will form the subject of the second part of the present Paper. 
(6) With regard to the direct absorption of ammonia or nitric acid from the air by 
plants themselves, we have little of either qualitative or quantitative evidence of any 
kind to guide us. Still, a few observations may be usefully hazarded, in passing, which 
may bear more or less directly upon the point. 
In our ripened Cereal crops, we find 1 part of Nitrogen to somewhere about 30 parts 
of carbon; and in our Leguminous crops, 1 part of Nitrogen to about 15 or fewer parts 
of carbon. It is supposed that the atmosphere, on the average, contains 1 part (or 
rather more) of carbon in the form of carbonic acid to 10,000 parts of air. We may 
perhaps assume, as an extreme amount, that the atmosphere contains only 1 part of 
Nitrogen in the form of ammonia to about 12,000,000 parts of air. Adopting these 
assumptions, there would obviously be, instead of only 30 or 15 times less Nitrogen 
than carbon (as in the respective crops), 1200 times less Nitrogen in the ambient air in 
the form of ammonia, than of carbon in the form of carbonic acid in the same medium. 
If, however, we were to adopt as more nearly the amount of ammonia in the air that 
found by M. G. VILLE (namely, only about one-fifth as much as we have assumed above), 
it would then appear that there were 6000 times less of Nitrogen in the air in the form 
of ammonia, than of carbon in that of carbonic acid. 
Taking the former or more favourable assumption of the two, the result would be, 
that the ambient atmosphere contained Nitrogen as ammonia, to carbon as carbonic 
acid, in a proportion 40 times less than that of Nitrogen to carbon in the Cereal pro- 
duce, and 80 times (or more) less than that of Nitrogen to carbon in the Leguminous 
produce. Adopting M. G. VILLE’s estimates, on the other hand, the proportion of the 
so-combined Nitrogen to the so-combined carbon, in the air, would be 200 times less 
than that of the Nitrogen to the carbon in the Cereal crops, and about 400 times less 
than that of the Nitrogen to the carbon in the Leguminous crops. 
