[20] See page 330. vol. i.
[22] Phil. Transact. 1813.
[23] Dr. Thomson has calculated that the quantity of coal exported yearly from this formation exceeds two millions of chaldrons; and he thinks it may be fairly stated, in round numbers, that, at the present rate of waste, it will continue to supply coal for a thousand years! Mr. Phillips, however, is inclined to deduct a century or two from this calculation.
[24] In all large collieries, the air is accelerated through the workings by placing furnaces, sometimes at the bottom, and sometimes at the top of the up-cast shaft; in aid of which, at Wall's-end Colliery, a powerful air-pump worked by a steam-engine is employed to quicken the draft: this alone draws out of the mines a thousand hogsheads of air every minute. Stoppings and trapdoors are also interposed in various parts of the workings, in order to give a direction to the draft.
[25] Sir James Lowther found a uniform current of this description produced in one of his mines for the space of two years and nine months. Phil. Trans, vol. 38. p. 112.
[26] Steel-mills are small machines, which give light by turning a cylinder of steel against a piece of flint. Sir James Lowther had observed early in the last century, that the fire-damp in its usual form was not inflammable by sparks from flint and steel; and it appears that a person in his employment invented the machine in question.
[27] It is unnecessary to enumerate the various schemes that have been proposed to prevent accidents from fire-damp. Some were unquestionably of value, and might, by their adoption, have diminished the frequency of explosions; others were visionary, or wholly impracticable. It was proposed, for instance, to fill the mine with an atmosphere of chlorine, which by entering into chemical union with the carburetted hydrogen, might disarm it of its power. Dr. Murray, in a paper published in the Transactions of the Royal Society of Edinburgh, suggests the use of a lamp that shall be supplied with air from the ground of the pit, by means of a long flexible tube, upon the false assumption that the fire-damp alone occupies the higher parts of the mine. Mr. W. Brandling also constructed a Safe-lamp, which, like that of Dr. Murray, was fed by air introduced through a long flexible tube reaching to the floor of the mine. In addition to which, he attached to the top of the lantern a pair of double bellows, by the aid of which he at the same time drew out the contaminated air from the interior of the lamp, and sucked in, through the flexible tube, a fresh portion to supply its place. To say nothing of the inefficacy and inconvenience of the long tube, the bellows possessed the additional objection of frequently puffing out the light.
One of the most active and intelligent members of the "Society for preventing accidents in Coal Mines," Dr. Clanny, had for some time paid particular attention to the object in contemplation. He first suggested the idea of an insulated lamp, of which an account appeared in the Philosophical Transactions for 1813. In 1815, he invented a steam safety-lamp, constructed of the strongest tinned iron, with thick flint glass in front. In this machine, the air of the coal mine passes in a current through a tube, and mixing with the steam, before it can arrive at the light, burns steadily in the wick of the lamp alone. This lamp has the valuable property of remaining cool. It has been much used in the Herrington Mill pit, the Whitefield pit, and the Engine pit.
[28] Quere—South Shields.