"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.