he root-crops.

It is often deficient in the soil, particularly where potatoes have been
long cultivated. One of the reasons why _plaster_ (sulphate of lime) is
so beneficial to the potato crop is undoubtedly that it supplies it with
sulphuric acid.

Sulphuric acid is commonly known by the name of _oil vitriol_, and may
be purchased for agricultural purposes at a low price. It may be used in
a very dilute form (weakened by mixing it with a large quantity of
water) to the compost heap, where it will change the ammonia to a
sulphate as soon as formed, and thus prevent its loss, as the sulphate
of ammonia is not volatile; and, being soluble in water, is useful to
plants. Some idea of the value of this compound may be formed from the
fact that manufacturers of manures are willing to pay seven cents per
lb., or even more, for sulphate of ammonia, to insure the success of
their fertilizers. Notwithstanding this, many farmers persist in
throwing away hundreds of pounds of _ammonia_ every year, as a tax for
their ignorance (or indolence), while a small tax in _money_--not more
valuable, nor more necessary to their success--for the support of common
schools, and the better education of the young, is too often unwillingly
paid.

[What is the effect of using too much sulphuric acid?]

If a tumbler full of sulphuric acid (costing a few cents), be thrown
into the tank of the compost heap once a month, the benefit to the
manure would be very great.

Where a deficiency of sulphuric acid in the soil is indicated by
analysis, it may be supplied in this way, or by the use of plaster or
refuse epsom salts.

Care is necessary that _too much_ sulphuric acid be not used, as it
would prevent the proper decomposition of manures, and would induce a
growth of sorrel in the soil by making it _sour_.

In many instances, it will be found profitable to use sulphuric acid in
the manufacture of super-phosphate of lime (as directed under the head
of 'phosphoric acid,') thus making it perform the double purpose of
preparing an available form of phosphate, and of supplying sulphur and
sulphuric acid to the plant.

PHOSPHORIC ACID.

[How large a part of the ashes of grain consists of phosphoric
acid?

Of what other substances does it form a leading ingredient?

How many pounds of sulphuric acid are contained in one hundred bushels
of wheat?]

We come now to the consideration of one of the most important of all
subjects connected with ag