In consequence of the agglutination and tumefaction, the passage of air, if this sort of coal be burnt in an open grate, is interrupted, the fire burns as it is called hollow, and would become extinguished if the top of the coal were not from time to time broken into with the poker.
The coke formed from this species of coal is more compact than that produced from the first sort of coal, and is well calculated for standing the blast of bellows in metallurgical operations. In respect to weight the second class of coal is considerably heavier than those of the first class, the difference amounts to not less than from twenty-eight pounds to thirty-three pounds in the sack of coal. A chaldron of some varieties of this class of coal, if the coals are in large lumps, weighs upwards of twenty-eight hundred weight.
The usual denomination by which the second class of coal is known in the London market, is that of _strong burning coal_. The following varieties are sufficiently known, Russel’s Walls-End; Bewick’s and Craister’s Walls-End; Brown Walls-End, Wellington Main, Temple Main, Heaton Main, Killingsworth Main, Percy Main, Benton Main, and some varieties of the Swansea coal.
The smaller kinds of coal of this class are preferred by smiths, because they stand the blast well. They make a caking fire so as to form a kind of hollow, space or oven, as the workmen call it. Some varieties abound in pyrites, and others are intersected with thin layers of slate and lime-stone. They require more heat for being carbonized than the first class, and the fluid obtained from it by distillation, contains a considerable portion of carbonate, sulphate, and hydrosulphuret of ammonia. They are well calculated for the production of coal gas; the coke which they produce is not very brittle, and will bear moving from place to place, without crumbling into dust.
The following table exhibits the maximum quantity of gas obtainable from the second class of coal.[8]
[8] Own Experiments, made at the Royal Mint Gas-Works.
One Chaldron of Coal, produces Cubic feet of Gas.
Newcastle coal, First variety, (Russel’s Wall’s End) 16,876 Second variety, (Bewick and Craister’s Wall’s End) 16,897 Third variety, (Heaton Main) 15,876 Fourth variety, (Killingsworth Main) 15,312 Fifth variety, (Benton Main) 14,812 Sixth variety, (Brown’s Wall’s End) 13,600 Seventh variety, (Mannor Main) 12,548 Eighth variety, (Bleyth) 12,096 Ninth variety, (Burdon Main) 13,608 Tenth variety, (Wears Wall’s End) 14,112 Eleventh variety, (Eden Main) 9,600 Twelfth variety, (Primrose Main) 8,348