etc., more healthy than when not so
supplied.

It has been observed that the extravagant use of plaster sometimes
induces the growth of _sorrel_. This is probably the case only where the
soil is deficient in lime. In such instances, the lime required by
plants is obtained by the decomposition of the plaster. The lime enters
into the construction of the plant, and the sulphuric acid remains
_free_, rendering the soil _sour_, and therefore in condition to produce
sorrel. In such a case, an application of _lime_ will correct the acid
by uniting with it and converting it into _plaster_.

CHLORIDE OF LIME.

[What does chloride of lime supply to plants?

How does it affect manures?

How may it be used?

How may magnesia be supplied, when wanting?

What care is necessary concerning the use of magnesia?]

_Chloride of lime_ is a compound of _lime and chlorine_. It furnishes
both of these constituents to plants, and it is an excellent absorbent
of ammonia and other gases arising from decomposition--hence its
usefulness in destroying bad odors, and in preserving fertilizing
matters for the use of crops.

It may be used like plaster, or in the decomposition of organic matters,
where it not only hastens decay, but absorbs and retains the escaping
gases. It will be recollected that _chloride of lime_ is one of the
products of the _lime and salt mixture_.

_Lime_ in combination with _phosphoric acid_ forms the valuable
_phosphate of lime_, of which so large a portion of the ash of grain,
and the bones of animals, is formed. This will be spoken of more at
length under the head of 'phosphoric acid.'

MAGNESIA.

Magnesia is a constituent of vegetable ashes, and is almost always
present in the soil in sufficient quantities. When analysis indicates
that it is needed, it may be applied in the form of _magnesian lime_, or
_refuse epsom salts_, which are composed of sulphuric acid and magnesia
(sulphate of magnesia).

The great care necessary concerning the use of magnesia is, not to apply
too much of it, it being, when in excess, as has been previously
remarked, injurious to the fertility of the soil. Some soils are
hopelessly barren from the fact that they contain too much magnesia.

ACIDS.

SULPHURIC ACID.

[What is sulphuric acid commonly called?

How may it be used?

How does it prevent the escape of ammonia?]

_Sulphuric acid_ is a very important constituent of vegetable ashes,
especially of oats and t