acid and two to three per cent. of nitrogen.

_Dissolved Bone Black._ Bone charcoal is used for refining sugar. It
is then turned over to the fertilizer manufacturers who sell it as
"Bone Black" or treat it with sulphuric acid and then put it on the
market as dissolved bone black.

The bone black contains thirty to thirty-six per cent. of insoluble
phosphoric acid.

The dissolved bone black contains 15 to 17 per cent. of available
phosphoric acid and 1 to 2 per cent. insoluble.

"_Thomas Slag_," "_Phosphate Slag_," "_Odorless Phosphate_."
Phosphorous is an impurity in certain iron ores. In the manufacture of
Bessemer steel this is extracted by the use of lime which melts in the
furnace, unites with the phosphorous and brings it away in the slag.
This slag is ground to a fine powder and used as a fertilizer. It
contains 11 to 23 per cent. of phosphoric acid, most of which is
available.

_Superphosphate._ The term superphosphate is applied to the phosphates
that have been treated with sulphuric acid to make the phosphoric acid
available. Dissolved bone, dissolved bone black, and the dissolved
phosphate rocks are superphosphates.

_Fish Scrap_, mentioned as a source of nitrogen, is also a valuable
source of phosphoric acid, containing 6 to 8 per cent., which is quite
readily available owing to the rapid decay of the scrap.

SOURCES OF POTASH

The chief sources of potash used for fertilizers are the potash salts
from the potash mines at Stassfurt, Germany, where there is an immense
deposit of rock salt and potash salts.

The principal products of these mines used in this country are the
crude salts:

_Kainite_, containing 12 per cent. of potash.

_Sylvinite_, containing 16 to 20 per cent. of potash, and the higher
grade salts manufactured from the crude salts:

_Muriate of Potash_, containing 50 per cent. potash.

_High grade Sulphate of Potash_, containing 50 per cent. potash.

_Low grade Sulphate of Potash_, containing 25 per cent. potash.

_Wood Ashes_, if well kept and not allowed to get wet and leach,
contain 4 to 9 per cent. of potash.

_Cotton Hull Ashes_ contain 20 to 30 per cent, of potash and 7 to 9
per cent. of phosphoric acid.

The potash in all these forms is soluble in water and equally
available to plants. The crude salts, kainite and sylvinite, and the
muriate contain chlorine and are not considered good for potatoes and
tobacco as the chlorine lowers the quality of these products.