Cannel coal, deserves to be placed at the head of this class; next to this, we may rank all those descriptions of coal known in the London market by the names of Hartley, Cowper’s Main, Tanfield Moor, Eighton Main, Blythe, and Pont Tops. It also includes the sort of coals found in several parts of Scotland, called Splent coal, and some of those raised on the Western Coast of England.
Most of the coals raised in Staffordshire ought likewise to be classed among this species of coal, but the line of distinction between these, and the classes subsequently named, cannot be accurately drawn.
The following table exhibits the maximum quantity of gas obtainable from the first class of coal.[4]
[4] Own Experiments, made at the Royal Mint Gas-Works.
| One Chaldron of Coal, produces | Cubic feet of Gas. |
|---|---|
| Scotch Cannel coal | 19,890 |
| Lancashire Wiggan coal | 19,608 |
| Yorkshire Cannel coal, | |
| (Wakefield) | 18,860 |
| Staffordshire coal,[5] | |
| First variety,[6] | 9,748 |
| Second variety, | 10,223 |
| Third variety, | 10,866 |
| Fourth variety, | 9,796 |
| Gloucestershire coal,[7] | |
| First variety, (Forest of Dean, High Delph) | 16,584 |
| Second variety, (Low Delph) | 12,852 |
| Third variety, (Middle Delph) | 12,096 |
| Newcastle coal, | |
| First variety, (Hartley) | 16,120 |
| Second variety, (Cowper’s High Main) | 15,876 |
| Third variety, (Tanfield Moor) | 16,920 |
| Fourth variety, (Pontops) | 15,112 |
[5] They require a much higher temperature, than is necessary for the decomposition of Newcastle coal.
[6] For the maximum quantity of gas produced from this and the three succeeding varieties of coal, I am indebted to J. Gostling, Esq. Proprietor of the Birmingham Gas Works.
[7] Most varieties afford a porous, and very friable coke.
The second class of coal, comprehends all those varieties which contain a less quantity of bitumen, and a larger quantity of carbon than the first class. They burn with a flame less bright and of a more yellowish colour, and the last portion of flame they are capable of yielding is always of a lambent blue colour, they become soft after having laid on the fire for some time, swell in bubbles and pass into a state of semi-fusion, they then cohere and coke, puff up and throw out tubercular scoriæ, with a hissing noise, accompanied with small jets of flame.
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.