THOMAS SLAG, PHOSPHATIC SLAG, BASIC SLAG, ODORLESS PHOSPHATE, or THOMAS PHOS PHATE POWDER. A by-product of the manufac ture of steel from phosphatic ores by the basic or Thomas process, in which phosphorus is elimi nated from the pig iron by means of basic (rich in lime) lining to the Bessemer converters and by adding lime to the molten pig iron. The slag is therefore rich in lime (about 15 per cent. in the free state and 40 per cent. combined with other substances). The phosphoric acid content of the product as found in the market is very variable, ranging from 10 to 25 per cent. Slag of average quality contains 15 to 20 per cent. of phosphoric acid. In good slag SO per cent. of this phosphoric acid should he available, as shown by the chemical methods of determining, availability, i.e. by treatment with a solution of citric acid or ammonium citrate. The phosphoric acid of slag, unlike that of superphosphates, is prac tically insoluble in water. Recently attempts have been made with some success to prepare a slag in which the phosphoric acid is more avail able by fusing the product as obtained from the converters at about 900° C. with sufficient silica (quartz) to convert the free lime into silicate. Such slag differs materially from the untreated product not only in containing a higher percent age of available phosphoric acid and of silica, but in being practically devoid of free lime. Basic slag is not suited to the manufacture of super phosphates and generally used without any treatment except fine grinding. Purchasers of Thomas slag should insist on its being finely ground, as the value of the material depends very largely upon its fineness.
Slag has been used in large quantities for agricultural purposes in Europe for a number of years—in 1899 1,655,000 tons. Of this 895,000
tons were used in Germany and 170.000 in France. In 1885 the use of this material was practically confined to Germany and amounted to only 5000 tons. Since the total consumption of phosphatic fertilizers in Germany in 1899 was 1,864,000 tons, and in France 245,0110 tons, nearly half of the phosphatic fertilizers used in these countries was Thomas slag. Slag has not been extensively introduced into the United States. Some has been manufactured at Pottstown, Pa., and put on the market under the name of 'odor less phosphate.' Experiments have shown slag to be a very valuable phosphatic fertilizer, and on account of its high percentage of lime espe cially suited to use on acid soils and those rich in organic matter. It would not be wise to use it freely on poor sandy soils deficient in organic matter. Experiments have indicated that slag and dissolved boneblack are about equally ef fective, taking into account the after-effects of the slag, while the cost of the latter is nearly twice that of the former.
Slag appears to he especially suited to legumi nous crops. Six hundred to one thousand pounds per acre is considered a liberal dressing. It should not he mixed with ammonium sulphate before use, since its high percentage of free lime is likely to cause a loss of ammonia by volatiliza tion. _Mixtures of the slag with other salts, such as muriate of potash and nitrate of soda, cake badly and are difficult to handle and dis tribute uniformly. See MANURES AND MANUR ING.