| 1885 109,400
1886 330,000 | 1886 75,100
1887 440,000 | 1887 83,100
1888 640,000 | 1888 103,100
1889 760,000 | 1889 120,000
1890 784,000 | 1890 114,000
1891 851,000 | 1891 121,000
1892 795,000 | 1892 115,000

CHAPTER X.

SULPHATE OF AMMONIA.

_Value of Ammonia as a Manure._

The value of ammonia salts as a manure has been long recognised; indeed
till recently ammonia was thought to be the most valuable form in which
nitrogen could be applied as a plant-food--a view, we may mention, held
by Liebig. While the plant, no doubt, can absorb its nitrogen in the
form of ammonia,[212] as well as in other forms, as we have already
pointed out in previous chapters, it is now fully recognised that
ammonia salts, when applied to the soil, are converted into nitrates.
Nitric acid, then, must be regarded as the most valuable, inasmuch as it
is the most rapidly assimilated form of nitrogen for the plant; but
next to nitric acid in value comes ammonia. Of the different forms of
ammonia available for manurial purposes, the only one used to a large
extent is sulphate.

_Sources of Sulphate of Ammonia._

The oldest, and what is still the chief source of this valuable salt, is
the gas-works, where it is obtained as one of the bye-products in the
manufacture of gas. It is also obtained to a lesser extent from shale,
iron, coke, and carbonising works. Bones, horn, leather, and certain
other animal substances rich in nitrogen, when subjected to dry
distillation, as is the case in certain manufactures, such as the
manufacture of bone-charcoal for use in sugar-refineries, and the
distillation of horn, &c., in the manufacture of prussiate of potash,
also constitute less abundant sources.

_Ammonia from Gas-works._

Coal contains on an average from a half to one and a half per cent of
nitrogen. When it is subjected to dry distillation, as is done in the
gas-works, the nitrogen which it contains is chiefly converted into
ammonia, and, in the process of purification of the gas, is removed in
the "gas-liquor,"[213] which contains about one per cent of ammonia.
The ammonia recovered from this liquor by distillation is then absorbed
in sulphuric acid. It may be pointed out that nothing like all the
nitrogen contained in the coal is re