LAMP-BLACK, a variety of carbon or charcoal in a state of minute division, prepared chiefly from the impure resin and other refuse left after the distillation of turpentine. These secondary products are burnt in iron pots, or in a furnace, with a supply of air inadequate to their complete combustion, and the dense smoke thus produced is passed into chambers lined with sheep skin, or with sacking, upon which the soot or lamp-black forms a deposit. It is swept off from time to time, and sold without any further preparation. In this state, however, it contains salts of ammonia, and certain resinous and bituminous matters, all of which may be driven off by heating the crude lamp-black to redness in a close vessel. Thus purified, the lamp-black is almost entirely pure carbon, and when heated in the air it will burn away with scarcely any residue. Lamp-black was formerly prepared by burning lamps fed with crude refuse oils, in a close chamber, and collecting the soot from the smoky flames in the manner above mentioned, whence the origin of the name lamp-black. The theory of its formation is simple: if a compound of hydrogen and carbon be raised to a temperature sufficient to convert it into an inflammable vapour, and enough oxygen be introduced to combine with the hydrogen only, water will be formed, and the carbon be deposited.
The chief demand for lamp-black is in the manufacture of black paint and printer's ink, for which it is often prepared by burning coal-tar. A coarse lamp-black, used in paying ships, &c., is also prepared from some kinds of coal. (c. 7.)