Iodide of Potassium, 0.44; Sulphuret of Sodium, 3.66.]

[Footnote G: Iodide of Potassium, 0.23.]

[Footnote H: Iodide of Potassium, 1.68.]

CHAPTER V.

THE SOIL--ITS CHEMICAL AND PHYSICAL CHARACTERS.

No department of agricultural chemistry is surrounded with greater
difficulties and uncertainties than that relating to the properties of
the soil. When chemistry began to be applied to agriculture, it was not
unnaturally supposed that the examination of the soil would enable us to
ascertain with certainty the mode in which it might be most
advantageously improved and cultivated, and when, as occasionally
happened, analysis revealed the absence of one or more of the essential
constituents of the plant in a barren soil, it indicated at once the
cause and the cure of the defect. But the expectations naturally formed
from the facts then observed have been as yet very partially fulfilled;
for, as our knowledge has advanced, it has become apparent that it is
only in rare instances that it is possible satisfactorily to connect
together the composition and the properties of a soil, and with each
advancement in the accuracy and minuteness of our analysis the
difficulties have been rather increased than diminished. Although it is
occasionally possible to predicate from its composition that a
particular soil will be incapable of supporting vegetation, it not
unfrequently happens that a fruitful and a barren soil are so similar
that it is impossible to distinguish them from one another, and cases
even occur in which the barren appears superior to the fertile soil. The
cause of this apparently anomalous phenomenon lies in the fact that
analysis, however minute, is unable to disclose all the conditions of
fertility, and that it must be supplemented by an examination of its
physical and other chemical properties, which are not indicated by
ordinary experiments. Of late years very considerable progress has been
made in the investigation of the properties of the soil, and many facts
of great importance have been discovered, but we are still unable to
assert that all the conditions of fertility are yet known, and the
practical application of those recently discovered is still very
imperfectly understood.

It must not be supposed that a careful analysis of a soil is without
value, for very important practical deductions may often be drawn from
it, and when this is not practicable it is not unfrequently due to its
being imperf