y to repeat here, that when the weakness of the straw or stalk
of plants grown on any soil indicates an inability in that soil to
supply the silicates required for strength, not more sand should be
added, but _alkalies_, to combine with the sand already contained in it,
and make _soluble silicates_ which are available to roots.

Sand is often necessary to stiff clays, as a _mechanical_ manure, to
loosen their texture and render them easier of cultivation, and more
favorable to the distribution of roots, and to the circulation of air
and water.

CHLORINE.

[How may chlorine be applied?]

_Chlorine_, a necessary constituent of plants, and often deficient in
the soil (as indicated by analysis), may be applied in the form of salt
(chloride of sodium), or chloride of lime. The former may be dissolved
in the water used to slake lime, and the latter may, with much
advantage, be sprinkled around stables and other places where
fertilizing gases are escaping, and, after being saturated with ammonia,
applied to the soil, thus serving a double purpose.

OXIDE OF IRON.

[How may the protoxide of iron be changed to peroxide?]

Nearly all soils contain sufficient quantities of _oxide of iron_, or
iron rust, so that this substance can hardly be required as a manure.

Some soils, however, contain the _prot_oxide of iron in such quantities
as to be injurious to plants,--see page 86. When this is the case, it is
necessary to plow the soil thoroughly, and use such other mechanical
means as shall render it open to the admission of air. The _prot_oxide
of iron will then take up more oxygen, and become the _per_oxide--which
is not only inoffensive, but is absolutely necessary to fertility.

OXIDE OF MANGANESE.

This can hardly be called an essential constituent of plants, and is
never taken into consideration in manuring lands.

VARIOUS OTHER MINERAL MANURES.

LEACHED ASHES.

[Why are leached ashes inferior to those that have not been
leached?

On what do the benefits of leached ashes depend?

Can these ingredients be more cheaply obtained in another form?

Why do unleached ashes, applied in the spring, sometimes cause grain to
lodge?]

Among the mineral manures which have not yet been mentioned--not coming
strictly under any of the preceding heads, is the one known as _leached
ashes_.

These are not without their benefits, though worth much less than
unleached ashes, which, besides the constituents of those wh