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A TREATISE ON GAS-LIGHT.

.perfect pit-coal; and by various shades, passesfrom the most inflammable canel-coal, intoblind, Kilkenny , or stone-coal; and, lastly,into a variety of earthy or stony substances ;which, although they are inflammable, do notmerit the appellation of coal.

Every body knows that when pit-coals areburning in our grates, a flame more or less-luminous issues from them, and that they fre-quently emit beautiful streams of flame remark-ably bright. But besides the flame, which isa peculiar gas in the state of combustion, heatexpels from coal an aqueous vapour, loadedwith several kinds of ammoniacal salts, a thickviscid fluid resembling tar, and some gases thatare not of a combustible nature. The conse-quence of which is, that the flame of a coal-fire is continually wavering and changing, bothin shape, as well as brilliance and in colour, sothat what one moment gave a beautiful brightlight, in the next, perhaps, is obscured by astream of thick smoke.

But if coals, instead of being suffered toburn in this way, are submitted to distillationin close vessels, all its immediate constituentparts may be collected. The bituminous part