Coke, if properly prepared, should consist of pure carbon.  Good coal should yield as much as 80 per cent. of coke, but owing to the unsatisfactory manner of its production, this proportion is seldom yielded, whilst the coke which is familiar to householders, being the residue left in the retorts after gas-making, usually contains so large a proportion of sulphur as to make its combustion almost offensive.  No doubt the result of its unsatisfactory preparation has been that it has failed to make its way into households as it should have done, but there is also another objection to its use, namely, the fact that, owing to the quantity of oxygen required in its combustion, it gives rise to feelings of suffocation where insufficient ventilation of the room is provided.

Large quantities of coke are, however, consumed in the feeding of furnace fires, and in the heating of boilers of locomotives, as well as in metallurgical operations; and in order to supply the demand, large quantities of coal are “coked,” a process by which the volatile products are completely combusted, pure coke remaining behind.  This process is therefore the direct opposite to that of “distillation,” by which the volatile products are carefully collected and re-distilled.

The sulphurous impurities which are always present in the coal, and which are, to a certain extent, retained in coke made at the gas-works, themselves have a value, which in these utilitarian days is not long likely to escape the attention of capitalists.  In coal, bands of bright shining iron pyrites are constantly seen, even in the homely scuttle, and when coal is washed, as it is in some places, the removal of the pyrites increases the value of the coal, whilst it has a value of its own.

The conversion of the sulphur which escapes from our chimneys into sulphuretted hydrogen, and then into sulphuric acid, or oil of vitriol, has already been referred to, and we can only hope that in these days when every available source of wealth is being looked up, and when there threatens to remain nothing which shall in the future be known as “waste,” that the atmosphere will be spared being longer the receptacle for the unowned and execrated brimstone of millions of fires and furnaces.

CHAPTER VII.

THE COAL SUPPLIES OF THE WORLD.

As compared with some of the American coal-fields, those of Britain are but small, both in extent and thickness.  They can be regarded as falling naturally into three principal areas.

  The northern coal-field, including those of Fife, Stirling, and Ayr
    in Scotland; Cumberland, Newcastle, and Durham in England; Tyrone
    in Ireland.

  The middle coal-field, all geologically in union, including those of
    Yorkshire, Derbyshire, Shropshire, Staffordshire, Flint, and
    Denbigh.

  The southern coal-field, including South Wales, Forest of Dean,
    Bristol, Dover, with an offshoot at Leinster, &c., and Millstreet,
    Cork.