Agricultural Chemistry. 
449 
jiower of tliis wafov for these substances having been increased hy the am- 
iiioniacal salts. The effect of the cnythij i)liusphates and of the soluble, silicates 
depends on the quantity of them in the soil ; their cflVct in a given time is 
pro]iortional to the quantity which enters the plant in that time. This a<;ain is 
proportional to the degree of their solubility in rain-water, and to the amount 
of rain-water absorbed by the plant." 
" Both properties — that of ammonia as a nutritive agent, or source of 
nitrogen, and that of theammoniacal salts as solvents — have certainly co-operated 
to give the hicreased produce ; for since the total produce, 28,431 lbs. of grain 
and straw, of the lot manured with ammoniacal salts, was to that of the nn- 
mamired land, 18,122 lbs. grain and straw, as three to two, and consequently 
the excess of the former was equal to half the amoimt of the latter, it is 
evident that this excess must have contained exactly as much silicate of potass 
and phosphates as existed in one-half the crop of the unnianured land. Now, 
since ammonia cannot replace these essential constituents of the wheat-j)lant, 
it follows, that, b}^ the agency of the ammoniacal salts, this entire additional 
quantity of mineral constituents was rendered soluble and available for the 
plant. These salts have enabled the rain-water, in equal volume, to dissolve 
and carry into the plant, in the same time, one-half more of these substances 
than was yielded, without ammoniacal salts, by the unmanured land." — Ih., pp, 
99-101. 
We are here tokl, then — in March, 1855 — that the efficacy of 
the salts of ammonia in our experiments is to be attributed in a 
great measure to their solvent action on the phosphates and silicates 
of the soil ; the increase of produce bein^ greatly due to the 
consequently increased supply of these minerals to the plant. 
The reader will imagine tlierefore our astonishment, when, in 
September of the same year, we heard Baron Liebig in the public 
discussion of our experiments, energetically maintain, that the 
presence in the soil of ammonia and its salts must reduce the 
solubility of the silicates ! We have since found, that he had then 
already published two papers in Germany, in the course of which 
he sought to establish the latter view. We are not disposed to 
dispute the probable truth of this amended conclusion. For, in 
experiments instituted wdth the view of testing the probability of 
Baron Liebig's previous assumption, we had found that water 
containing salts of ammonia, when percolated through a given 
bulk of soil, dissolved less silica than pure water so percolated. 
At the same time, however, we must say, that we cannot admit 
the legitimacy of deductions from experiments made upon pure 
silicates out of the soil, as to what would happen under the com- 
plicated and little understood chemical conditions of cultivated 
soils. 
At any rate, however, we must conclude, that Baron Liebig's 
explanation of the efficacy of ammonia-salts in our experiments, 
so far as it supposed an increased supply to the plant of silica 
— the characteristic mineral constituent of the crops to which 
ammonia as a manure is peculiarly adapted — is now abandoned ! 
But what of the phosphates ? We will neither assert nor deny, 
