ey can be easily decomposed if they are heated or
brought into contact with some other substance which will give rise to
chemical action. Sulphate of ammonia is a salt that is very easily
decomposed. This is due to the fact that its base, ammonia, is very
volatile, and not capable of being held very firmly by an acid, even by
sulphuric, which is among the least volatile of all the common acids.
If, therefore, sulphate of ammonia be heated above the boiling-point of
water, or brought in contact with any other substance which will give
rise to chemical action, it is easily decomposed. Now a salt may be
acted upon by a base or an acid or another salt. When it is brought in
contact with a base, if the base with which it is brought in contact be
a stronger base than the base of the salt, the salt is decomposed, and a
new salt is formed. The acid, in short, exchanges its old base for the
new one.

_Effect of Lime on Ammonia Salt._

This is exactly what takes place when the base lime comes in contact
with an ammonium salt, such as sulphate of ammonia. The sulphuric acid
exchanges its old base, ammonia, for the stronger base, lime, and
sulphate of lime is formed, and ammonia is set free as a gas, and
escapes and is lost. Sulphate of ammonia, or any substance in which
there is an ammonia salt, must never be brought in contact with free
lime, otherwise the ammonia will be lost, and should be harrowed in on
chalky soils for this reason.

It is different entirely with gypsum--which is sulphate of lime--or
phosphate of lime, both of which may be safely mixed with sulphate of
ammonia without any danger of escape of ammonia. It follows from the
above that a mixture which must on no account be tried is slag phosphate
and sulphate of ammonia. This is because the slag phosphate contains a
large percentage of free lime, which would at once, on being brought in
contact with the sulphate of ammonia, decompose it, and cause the
ammonia to be lost. For this same reason guano must not be mixed with
slag. It is perhaps unnecessary, however, to warn one against so doing,
as it is not likely such a mixture would be made, as the ratio of
phosphoric acid to nitrogen in guanos is generally greater than is
required. If it be desired to mix the slag with a quickly available form
of nitrogen, nitrate of soda is not liable to loss; although for other
reasons it is not desirable to apply nitrate of soda along with the
slag, as the former manure shou