Agricultural Chemistry. 
4G3 
but which, however, is the clear vvaj of escape from his previous 
applications of his doctrines, and a net large enough to include 
many now established facts inconsistent with those applications, 
is insisted upon much more at length in Baron Liebig's recent 
reply to the criticisms of his ' Principles ' by Professor Wolff. 
In like manner, the careful reader will observe throughout all 
Baron Liebig's writings in this discussion, that, whenever there 
is a fact to be admitted, or a deviation from the exact expression 
previously given to his views to be conceded, we are first fa- 
voured with a general or abstract statement ; perhaps obviously 
true, and perhaps so little differing from previous forms of ex- 
pression in individual sentences of his works, as to pass unobserved, 
and yet sufficient to claim the fact or conclusion which he has 
to record and admit, as but an obvious consequence. The fol- 
lowing is a further illustration of this mode of ignoring the ex- 
perimental evidence and conclusions of others, and of netting 
the whole as an obvious consequence from his own principles. 
The reader need scarcely be reminded of Baron Liebig's argu- 
ment on Boussingault's rotations, viz., that the nitrogen of his 
manure had done nothing ; and that if the latter had been 
burnt, and its nitrogen expelled, the produce would have been 
the same ; — that, in defining agriculture as distinguished from 
normal vegetation, he has said, that the nitrogen yielded to the 
latter by the atmosphere was " quite sufficient for the purposes 
of agriculture — and that, speaking of produce grown under cul- 
tivation, that is, in agricultural quantity, he has said — " Surely 
thecerealia and leguminous plants which we cultivate must derive 
their carbon and nitrogen from the same source whence the 
graminese and leguminous plants of the meadows obtain them ! " 
But what are we now told? And how is the very opposite of this, 
the clear recognition of which we have maintained to be the very 
key to advancement in agricultural science, now swept into accord- 
ance with Baron Liebig's own prineiples by general and abstract 
statements, obviously true, and put apparently with little reference 
to any point in dispute ? 
" B\it the quaniity or amount of produce is in proportion to two factors, 
namely, the atmosjiheric food of plants, and their terrestriul or mineral food. 
This quantity depends on the presence of both, and on their co-operation in 
due proportion, and in the proper time. 
" If the amount of one of these factors — the mineral food of jMnts — be 
increased, while that of the other — the carbonic acid and ammonia, which 
can be conveyed to the plants by means of the atmosphere — remain unchanged, 
the amount of carbonised and nitrogenised produce cannot thereby increase; 
but the crops, in this case, will vary with the absorbing or active surface of 
the plants cultivated on the land." — Frincixdes, p. 70. 
He then goes on to state that " the air contains a very limited 
amount of carbonic acid and ammonia," and that — 
2 H 2 
