The production of the _gas light_ is easily effected in miniature, by putting common coal, pounded small, into the bowl of a tobacco─pipe, and closely covering this with clay made into a stiff lute with water. When the clay is dry, the bowl of the pipe must be put into the fire, and there heated gradually. In a few minutes a stream of gas will issue from the end of the pipe. This may be set on fire with a piece of paper, and will burn with a bright flame. When the gas is no longer disengaged, there will be found in the bowl of the pipe the remains of the coals, in the form of coke. It is estimated that one chaldron of good coals will afford from 17,000, to 20,000 cubical feet of gas; and that one of the large burners in the shops of London, consumes about four cubical feet per hour. _Soot_ is produced from the smoke of burned coal, and is used as a manure for cold, moist, and clayey meadows and pastures: and pounded coal has been applied to the same purpose in some parts of the Continent. By a process called charring, coal is divested of its humid, acid, and bituminous particles, and is converted into a kind of cinder called _coke_. This is employed in cases where intense heat is requisite, as for the smelting of iron ore; and likewise where acid and bituminous particles of coal would be detrimental, as in the drying of malt. What is usually termed _culm_ is the refuse or dusty coal, produced in working the common coals. It contains much earthy matter, will not kindle in an ordinary fire─place, but produces considerable heat and flame in a furnace, where a strong current of air is introduced. In England it is exempted from the high duty imposed on other coals, and is sold at a very low price. It is used for burning lime, making salt, and in steam engines. 219. _CANNEL COAL is of black colour, with little lustre, is not laminar, but breaks in any direction, like pitch, and does not stain the fingers._ This highly inflammable kind of coal is found abundantly in the neighbourhood of Wigan, in Lancashire, where there is an entire stratum of it about four feet in thickness. It is also found near Whitehaven, in some of the pits at Newcastle, and in some parts of Scotland. Doubts have been entertained respecting the name of this coal; but when it is recollected that in Lancashire, whence it is chiefly brought, the word candle is usually pronounced with the omission of the letter _d_, and that, in many instances, the coal is used by the poor as a substitute for candles, these will be immediately removed. In Scotland it has the name of _parrot coal_.