488 
Afjricultural Chemistry. 
It should be mentioned, that in the fourth and last edition 
of Baron Liebig's main work, in the chapter entirely de- 
voted to an explanation of the beneficial effects of fallow and 
the mechanical operations of the farm, he does not say one 
single word in reference to the accumulation by these means, 
of available atmospheric food— nitrogen — within the soil it- 
self; but only of the greater supplies of the mineral or soil- 
proper constituents, which are thereby rendered soluble and 
available for the plants. We have ourselves, on more than one 
occasion, called attention to the former influences ; and also to 
the fact, that a study of the properties of soils in relation to the 
accumulation of the atmospheric food of plants, promised to be 
of more value to agriculture, than that of the mere determination 
of their percentage composition in the mineral food of plants ; 
and, to the opinion that this is a field of inquiry highly deserving 
of the attention of the agricultural chemist, we are happy to have 
now the sanction of Baron Liebig himself. Thus he noio says : — 
" Fallow is tlie time during which this weathering .takes place. During 
fallow, carbonic acid and ammonia are convej'ed to the soil by the rain and 
the air ; the ammonia remains in the soil, if substances be present in due 
proportion which deprive it of its volatility by combining with it." — Prin- 
ciples, p. 2t), prop. 26. 
And again : — • 
" But so to prepare the soil as to enable if to extract from the air, and the 
other sources offered to plants by nature, and to condense in its ]iroducts a 
maximinn of nitrogen, — this, indeed, is a iiroblem worthy of scientific agri- 
culture." ! — I'rincijjles, p. 105. 
Here again, in his 26th, as well as in his 14th proposi- 
tion, there is evidence that Baron Liebig's views have been 
strikingly " corrected and enlarged " ! This influence oi fallow 
is then we say, not that, there being within the soil a 
more liberal provision of the mineral food of plants, they, 
the plants, are enabled to absorb more nitrogen from atmos- 
pheric sources ; but it is, so far as accumulation of nitrogen 
is concerned, that the soil itself has absorbed it from atmos- 
pheric sources ; without which condensation within the soil, of 
the atmospheric food of plants, no adequate increase of produce 
of grain would have been obtained, however great might have 
been the increased supply of the soil-proper or mineral lood of the 
plants. 
Our next endeavour will be to trace the chemical statistics of 
an actual ratation of crops itself, which will enable us to form a 
judgment, whether the facts which are thus elicited, taken in 
connec tion with those which have been indicated with regard to 
the action of manures on the individual crops, do not afford us 
some insight into the chemical principles upon which that main 
arm of agriculture, rotation, is founded. Before, however, enter- 
