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 |
The third and last class of coals includes those which are destitute of bitumen, being chiefly composed of carbon in a peculiar state of aggregation, evidently combined chemically with much earthy matter. Coals of this class require a still higher temperature to become ignited than any of the former classes, they emit little or no smoke. When laid on a fire they burn away with a feeble lambent flame, indeed some varieties give no flame at all, but burn merely with a red glow, somewhat like charcoal, and at length become consumed without caking. They leave a small portion of heavy ashes.
When submitted to distillation they afford little or no tar; of a consistence almost resembling pitch, and a gaseous fluid chiefly composed of gaseous oxide carbon and hydrogen gas. It is scarcely necessary to add that they are altogether unfit to be employed for the manufacture of coal gas. The Kilkenny, Welch, and stone or hard coal belong to this class. They require a strong draught when burnt in an open fire-grate, and the large quantity of gaseous oxide of carbon which they furnish during their combustion is extremely offensive. This is particularly the case with Kilkenny coal. The Welch stone or hard coal is better adapted for culinary purposes, and there is reason to believe that this species of coal might be rendered useful in the smelting of iron ore, by a slight modification in the metallurgic process employed for extracting the metal from its ore, but to eradicate prejudice, and to alter established practices is a work which nothing but time can effect. This species of coal is sent all over the kingdom; it is well calculated for the operations of drying malt and hops, and its small coal or culm has been found a more economical fuel, than Newcastle and Sunderland coals, for the burning of lime and bricks, and for all other processes where no blazing fuel is required.
The following table exhibits the maximum quantity of gas obtainable from this class of coals.
| One Chaldron of Coal, produces | Cubic feet of Gas. |
|---|---|
| Welch coal. First variety, from Tramsaren, near Kidwelly,[9] | 2,116 |
| Second variety, from the yard vein at the same place | 1,656 |
| Third variety, from Blenew, near Llandillo | 1,416 |
| Fourth variety, from Rhos, near Ponty Barren | 1,272 |
| Fifth variety, from the Vale of Gwendrath | 1,292 |
| Sixth variety, from ditto | 1,486 |