The Romance of Modern Chemistry

MORE ABOUT FUEL the manufacture of coal gas, is prepared in large quan- tities for its own sake. It is extensively used in metal- lurgical operations, that is, in the production of metals from their ores. The coke required for this purpose must be specially dense, and as free as possible from sulphur and ash. Gas coke does not adequately fulfil these conditions, and in Great Britain as much as twelve million tons of coal are destructively distilled every year in special ovens in order to get coke suitable for metal- lurgical purposes. This is frequently described as oven coke. The use of coke in metallurgical operations is readily understood. In iron-smelting, for instance, the ore consists mainly of iron oxide, and when this is heated in the blast furnace with coke, the oxygen prefers to be in partnership with the carbon rather than with the iron, so that the latter is liberated, and is obtained from the blast furnace as molten metal. Coal is not the only naturally occurring substance that is subjected to destructive distillation. In Scotland there is a very considerable industry founded on the winning of fuel oil by the destructive distillation of shale. This is a carbonaceous substance which differs from coal in that it contains a very much larger proportion, sometimes as much as 70 per cent., of mineral matter or ash. By the destructive distillation of a ton of shale about thirty gallons of crude oil can be obtained, which by further treatment is made to yield paraffin oil, lubricating oil, and paraffin wax. Attempts have been made also to subject peat to de- structive distillation, but these have generally ended in failure. The difficulties, however, are now being over- come, and quite recently a promising development has 149