148 
The first experiments of Berthelot date from 1885. Their object 
ras the fixation of nitrogen by denuded soils, leaving out, conse- 
ike all idea of vegetation. The soils used for the purpose were 
chosen from among the poorest in nitrogen. They were sandy clays 
taken from Mendon or from Sevres, below the level of the quarries, 
or, again, porcelain earths, crude kaolins not yet crushed in the mills. 
These soils, four in number, were submitted to five series of ex- 
periments. They were left to themselves in glazed pots, either 
within a well-closed room or in the open air in a meadow, either 
without shelter or under a little glass roof, merely to protect them 
from vertical rains, or on the top of a tower 29 meters above the 
ground and without any shelter, or finally, in corked flasks, so as to 
exclude all possibility of absorption of ammoniacal or nitric vapors. 
In the fifth series of experiments the same soils had first been ex- 
posed to a temperature of 100°, so as to destroy from the first all the 
organic germs that they might contain. The quantity of nitrogen, de- 
termined with great precision in each of the samples at the very 
beginning of the experiment, was again analyzed after two months, 
and again after remaining five months under the conditions indi- 
‘ated above, allowance being made for exterior additions attribut- 
able to air and to the rains when the pots were not sheltered. 
The results obtained did not leave the shghtest doubt. In every 
case in which the earth had been left in its normal state it had be- 
come enriched, and sometimes to a very great extent more than 
doubling the quantity of the initial nitrogen; when, on the contr ary, 
the soil had been sterilized by heat, it became constantly more 
impoverished. In a word, then, poor clayey soils are able to absorb 
atmospheric nitrogen directly. This absorption is not accompanied 
by any increase in the previous proportions of ammonia or of nitric 
acid; it is, then, due to the formation of complex organic substances. 
Finally, it is the work of a micro-organism, since it ceases to be pro- 
duced ‘as soon as the soil has been sterilized. 
To what sum per hectare does such a fertilization correspond 4 
Berthelot estimates at 20 or 30 kilograms for a thickness of one 
decimeter of soil. Hence for a thickness of 0.35 meter it would 
suffice to compensate for the losses inherent to drainage and cultiva- 
tion; but before going further it is well to remark that the experi- 
ments which we have “just described relate to particularly poor soils, 
which are therefore of a nature to enrich: themselves. In truly 
arable soils, averaging from 1 to 2 grams of nitrogen per kilogram, 
Berthelot has also observed a perceptible fixing of nitrogen, which, 
however, is relatively less than in sandy clays, and it is probable 
that this phenomenon would cease to be apparent after a certain 
limit, which, doubtless, is not very high. 
The conditions which, according: to Berthelot, apear the most 
favorable to the fixing of nitrogen by the naked soil are: 
1. The presence ofa quantity of water comprised between 3 and 15 
per cent of total saturation ; 
2. A sufficient porosity to assure the free penetration of air 
throughout the whole mass of earth; 
A temperature of between 10° and 40° C. 
These conditions define the microbe which secretes or fixes the 
nitrogen as an aerobic organism (1. e., one that feeds on the atmos- 
phere or is aerobiotic), 
