xviii

We know by analyses of Gregory, Way, Boussingault and Liebig,
that a wheat crop of 32 bushels at 62 lbs. contains of:

Grain 1,984 lbs. containing Phos. Acid, 19.0 lbs.
Straw 3,360 lbs. "          " "         5.4 lbs.

Chaff 400 lbs. "          " "         2.1 lbs.

Total amount of Phosphoric Acid 26.5 lbs.

If we now take a crop of 32 bushels at 62 lbs. for an average
crop, which a wheat soil ought to produce, and to which any wheat
soil can be improved, then it is necessary as above mentioned, that
it must contain 26.5, or we will say 30 lbs. of Phosphoric Acid, if
it shall be able to produce the above crop.

The weight of an average acre of soil one foot deep, is 3000
tons, according to the mean specific gravity of 16 varieties of soil,
dried in the air, which was 2.44, as ascertained by Dr. Krocker.

These two statements show us at once the way in which soils
ought to be treated for detecting the presence, and at the same
time the approximate quantity of Phosphoric Acid in them.
If 3000 tons, or 6,000,000 lbs. of soil, (one acre) ought to con-
tain 30 lbs. of Phosphoric Acid to produce a fair crop of wheat,
then every part of this mass ought to contain 1-200.000 of Phos-
phoric Acid. Or if we dissolve the Phosphoric Acid in a certain
quantity of this mass by a solvent of equal weight, the solution
obtained will also contain 1-200.000 of Phosphoric Acid; or by-
evaporating the same to 1-4, a solution will be obtained which
contains 1 500-000 of Phosphoric Acid, an amount which can be
detected by molybdate of ammonia, as above stated.

For the analysis of soils, the most convenient quantity to be taken
is about 3-4 of a pound, which is to be treated with the same quan-
tity of water, acidulated with nitric acid and then heated in a water-
bath for about an hour.

For the purpose of testing a soil for its sufficiency or deficiency
in Phosphoric Acid, a certain portion of the filtered solution of the
soil is to be evaporated to one-fourth, (an excess of Nitric Acid
being present) and then tested with Molybdate of Ammonia.

If a visible precipitation takes place, then 30 lbs. of Phosphoric
Acid at least exist in the examined soil; 60 lbs. of Phosphoric Acid
if evaporated to one-half; 90 lbs. of Phosphoric Acid if evaporated
to three quarters; 120 lbs. if not at all evaporated, &c.

Determination of Sulphuric Acid.

For the determination of Sulphuric Acid we can apply a still
finer and more sensible re-agent than even for that of Phosphoric
Acid. Experiments which were made on this subject resulted in
the observation, that in a solution of sulphate of soda which con-