explanation of its action, and
has not been supported by definite experiment. Although little effect
has been observed from salt, it deserves a more accurate investigation,
as not withstanding the extent to which it has been employed, we are
singularly deficient in definite experiments with it.

_Carbonates of Potash and Soda_ have only been tried experimentally, and
that to a small extent, nor is it likely that they will ever come into
use, owing to their high price. The remarks we have made in the section
on the ashes of plants regarding the subordinate value of soda, will
enable the reader to see that greater effects are to be anticipated
from the former than from the latter of these salts. They _may_,
however, exert a chemical action on the soil, altogether independent of
their absorption by the plant, but its nature and amount are still to
determine.

_Silicates of Potash and Soda_ have been employed with the view of
supplying silica to the plant, but the results have been far from
satisfactory. This may perhaps have been due to the doubtful nature of
the commercial article, but now that silicate of soda can be obtained of
good quality, it is desirable that the experiments should be repeated.
It is said to have produced good effects on the potato.

_Sulphate of Magnesia_ can be obtained at a low cost, and has been used
as a manure in some instances with very marked success. It has been
chiefly applied as a top-dressing to clover hay, but it seems probable
that it might prove a useful application to the cereals, the ash of
which is peculiarly rich in magnesia.

Many other saline substances have been tried as manures; but in most
instances on too limited a scale to permit any definite conclusions as
to their value. The experiments have also been too frequently performed
without the precautions necessary to exclude fallacy, so that the
results already arrived at must not be accepted as established facts,
but rather as indications of the direction in which further
investigation would be valuable. There is little doubt that many of
these substances might be usefully employed, if the conditions necessary
for their successful application were eliminated; and no subject is at
present more deserving of elucidation by careful and well-devised field
experiments.

_Phosphate of Lime._--The use of bones in their natural state as a
manure has been already adverted to, and it was stated, that though
their value depended mai