Agricultural Chemistry. 
423 
field that physical condition wliicli renders possible and increases tlie assimi- 
lation of these ingredients hy the plant ; he must remove the impediments 
which diminish their effect." — Address — ' On the Principles of Arfifcial 
Manuring ' — p. IG. 
" The duration of the fertility of a field depends on the amount of the 
mineral aliments of plauts contained in it, and its productive power for a given 
time is in a direct proportion to that part of its composition which possesses 
the capacity of being taken up by the plant." — Address, p. 10. 
" Pi-acticc in agi'iculture has taught us that the amount of vegetable matters 
on a given surface increases with the sujiply of certain substances, which 
WERE ORIGINAL COKSTIT0EKTS OF THE SAME SURFACE OF THE SOIL, and had 
been removed from it by means of plants. The excrements of men and of 
animals arise from plants ; they are exactly the materials which, durmg the 
life of the animal, or after its death, obtain again the same form that they 
possessed as constituents of the soil. 
" We know that the atmosphere does not contain these materials, and that 
it docs not replace them ; we know further that, by their removal from the 
soil, an ineijuality of production is occasioned, and, finally, even a want of 
fertility; but that, &?/ the restoration of these materials, the fertiUtij may he 
sustained, and even increased." — 4</i Edition, p. 1()4. 
" Hie fertilising piower of manure can he determined hy weight, as its effect 
is in a direct ratio to its amoimi in the mineral elements of the food of plants." 
— Address, ik 11. 
The above quotations show what was the relative importance 
attached by Baron Liebig to the nitrogenous and the mineral 
constituents of manure respectively ; and how far he has been 
misrepresented on this point, by the quotation from him of 
Avhich he so much complains ; namely, that " the crojis on a 
field diminish or increase in exact proportion to the diminution or 
increase of the mineral substances conveyed to it in manure.^' 
We shall now proceed to point out what were the means in- 
sisted upon by Baron Liebig, as necessary to the maintenance and 
increase of production of cultivated land ; by which a judgment 
may be formed, whether "it never occurred" to him "to assert 
that the land of Great Britain was deficient in the substances 
which are found together in the ashes of the crops raised on it." 
Baron Liebig says : — 
" Is it conceivable, that a rich fertile land, with a flourishing trade, which 
has for centuries exported the products of its soil in the form of cattle and of 
corn, can retain its fertility, if the same trade do not restore to its land, in the 
form of manure, the constituents abstracted from it, and which cannot be re- 
placed by the atmosphere ? In such a case, would not the same fate await 
this land as that which befel Virginia, upon the soil of which wheat and 
tobacco can no longer be cultivated.?" — ith Edition, p. 164, 165. 
Speaking of phosphate of lime and the alkaline phosphates, 
he says : — 
" An enormous quantity of these substances indispensable to the nourish- 
ment of plants, is annually withdrawn from the soil and carried into great 
towns in the shape of flour, cattle, &c. It is certain that this incessant 
removal of the phosphates must tend to exhaust the land and diminish its 
capability of producing grain. The fields of Great Britain are in a state of 
progressive exhaustion'from this cause, . . . ." — Letters, p. 522. 
