66                                       

constituents. But bones contain, when fresh, from 40 to 50 per
cent, of organic matter, which is capable of affording about six per
cent, of ammonia by its decomposition. Bone dust as sold in the
market usually contains from 60 to 70 per cent, of phosphate of
lime. The drying, boiling and sometimes burning of the bones
renders the quantity of mineral matter comparatively greater than
is found in fresh bones. Besides in bones, combinations of phos-
phoric acid are found in wood ashes, in guanos, in poudrette, and
in very small quantities in some marls and limestones. To supply
phosphates we should either look to bones, to Mexican or other
phosphatic guanos.

Mode of Application —The manner and form in which a manure
is applied is frequently of as much importance as the manure itself.
Bone dust is comparatively of high cost, and very often the form
in which it may be applied is of great consequence. Bone dust
should never be applied except in the finest powder, or dissolved
in sulphuric acid, and forming the well known superphosphate,
of Lime. True economy, which is the judicious application
of means, requires that it should always be dissolved before
using it.                                                                                               

In agriculture we have to deal with two varieties of the phos-
phate of lime; one, the bone earth phosphate or bone dust, in its
natural form; the other, the acid phosphate of lime, superphos-
phate, or biphosphate. One of the greatest boons which science
has conferred on agriculture is that of dissolving bones before using
them. In the condition in which bones originally exist, and even
when they are ground to the finest powder, they are still compara-
tively insoluble, and we must apply a large quantity to supply the
growing crop. When dissolved by means of sulphuric acid they are
then very soluble, can be spread much more equally over the soil,
and will exert a much speedier influence on the crop. It is not
out of place here to speak of some of the more important changes
which take place on the addition of sulphuric acid to bone dust or
phosphate of lime. Pure neutral phosphate of lime contains of

Phosphoric acid,....................................48.50 per cent.

Lime,................................................51.50 per cent.

Biphosphate of lime is composed of

Phosphoric acid,....................................71.50 per cent.

Lime,.................................................28.50 per cent.

This latter compound is very soluble and is produced in this
way. In chemistry we have what are called weak and strong
acids. When a weak acid is united to a base, a stronger acid will
expel it and seize on the base itself. We have a familiar example