SJE J. B. LAWES AND PROFESSOB J. H. GILBERT ON THE 
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2. The Evidence relating to the Fixation of Free Nitrogen. 
In the experiments of M. Berthelot, in all of which the gains of nitrogen are 
comparatively small, they have in some cases been attributed to electrical action, and 
in others to the agency of micro-organisms within the soil. 
M. Berthelot first showed that free nitrogen was fixed by various organic 
compounds under the influence of the silent electric discharge, at the ordinary 
temperature ; and he suggested that such actions probably take place in the air 
during storms, and when the atmosphere is charged with electricity, organic matters 
absorbing nitrogen and oxygen. He also experimented with currents of much weaker 
tension, more comparable with those incessantly occurring in the air, and in all cases 
he found that nitrogen was fixed by the organic substance. The gains were in amount 
such as would explain the source of the nitrogen which be considers crops must derive 
from the atmosphere. 
Subsequently, he found that free nitrogen was brought into combination by 
argillaceous soils, when exposed in their natural condition, but not when they were 
sterilised. He also found gain when the natural soils were enclosed. He considered 
the results showed that there was gain of nitrogen quite independently of any absorp¬ 
tion of combined nitrogen; in fact that there was fixation of free nitrogen due to 
living organisms. He further considered that such gains, not only serve as compensa¬ 
tion for exhaustion by cropping, &c., but explain how originally sterile argillaceous 
soils eventually become vegetable moulds. 
He also made experiments on the fixation of free nitrogen by vegetable earth 
supporting vegetation ; and he found that there was a gain about equally divided 
between the soil and the plant, the latter having taken it up from the soil, which he 
considers is the true source of gain. 
The results obtained under the influence of the silent discharge in bringing free 
nitrogen into combination with certain vegetable principles, of course owed their 
special interest to the inference that thus free nitrogen might be brought into 
combination within the plant; but M. Berthelot now considers it doubtful whether 
the higher plants do bring free nitrogen into combination at all. Obviously, however, 
if there are organic compounds within the soil which have the power of brmging free 
nitrogen into combination under the influence of electricity, the soil may be the 
source, and yet the agent may be the feeble electric current. But, so far as it is 
assumed that free nitrogen is brought into combination in the atmosphere itself, the 
resulting compounds will be found in the air, and in the aqueous depositions from it; 
and the limit of the amount of combined nitrogen so available over a given area, in 
Eui’ope at any rate, is pretty well known. 
In conclusion, although it must be admitted that M. Berthelot carefully 
considered, and endeavoured to estimate, all other sources than free nitrogen, yet the 
conditions of risk and exposure to accidental sources of gain, in experiments in open 
