450 
Afjricultural Chemistry. 
that these important mineral constituents may be rendered more 
soluble in the soil, in a given amount of water, provided this 
■water contain ammoniacal salts. But, whetlicr or not the increase 
in the produce of grain and straw in our experiments, was in any 
important degree due to this cause, is quite another question. 
Uj)()n this point some opinion may be formed from the following 
considerations : — 
How is it, we would ask — if, in the experiments where 
ammonia-salts alone were employed for a series of years, " only 
a small part of the ammonia acted by its nutritive property, and 
by far the greater part by its solvent power for phosphates " — 
how is it, we would ask, if this were the case, that the addition 
of a very much \n.vgex direct sujiplij of phosphates than the increase 
of crop could require, indeed in an amount and in such a form 
of easy solubility as to yield extraordinary results with some 
other crops than the cereals, should, with the latter, when used 
without ammonia, give scarcely any increase whatever? In 
other words, are we to suppose a greater amount of phosphates 
to be rendered soluble from the stores of the soil itself, by the 
solvent action of the ammonia-salts employed, than by the clii-ect 
use, in an easily soluble form, of many tijnes more phosphates than 
the increase of crop could require ? On this point we may state, 
that the increase of produce on plot 10a contained an annual 
average of 6 to 7 lbs. of phosphoric acid ; whilst ten times that 
amount was the general dose of that acid supplied to tlie soil in 
our experiments when mineial manures were employed — a large 
part of it existing, when added to the soil, in that form of easy 
solubility as superphospliate of lime, which is found so efficient 
for otlier crops than the cereals, the remainder existing as very 
finely powdered earthy phosphate. 
Would it not be both more candid and more consistent, instead 
of thus wrestling to the last to maintain the shadow of an obvi- 
ously half -abandoned theory, to attribute the increased assimila- 
tion of minerals on a given space of ground, which is necessarily 
incident to an increase of croji, rather to a multiplication of the 
feeders of the plants, and an increased vigour of growth under 
the influence of nitrogenous supply, which, by virtue of the 
larger amount of soil-solution which must be absorbed, enables 
them to take up with it more of those minerals which were 
obviously neither wanting nor insoluble ; although they cannot 
be assimilated by the cereals beyond a limited amount (varying 
with atmospheric supplies), unless nitrogen in an available form 
be at the same time provided within the soil itself i 
We proceed next to show how, the effects of available nitrogen 
supplied to the soil being necessarily admitted, the fact of its 
being thereby enabled to yield an increase of produce, is not to 
