An especially fine quality of lamp black is obtained from bone-oil, deprived of' the ammonia with which it is always contaminated. It is manufac tured on a commercial scale by means of the apparatus shown in Figs. 314 and 315. The oil is contained in the lamp A and kept at a constant level by means of the globular vessel B, which is.also filled with oil and inverted over A. The oil flows from the lamp into the tube C, which is bent upwards at the further extremity on a level with the oil in the lamp. A cotton wick is supplied to the bent end of the tube, as well as a little spout D, for conducting away any oil that may overflow into the receptacle E placed beneath. A conical hood a surreunds the flame of the lamp and terminates in a tube b, through which are conveyed the sooty products of the combustion of the oil into the wide lateral tube c, arranged to accommodate the smoke from about a dozen such lamps placed at intervals of about 6 ft., as indicated in the figures. The effect of this wide tube c is not only to cool the smolea but also to collect the water and other liquids condensed. The smoke and vapours pass hence into d, the first of a series of sacks made of closely woven linen, about 10 or 12 ft. long and 3 ft. in diameter, closed at the bottom with a trap or slide e, and formed at the upper and lower ends of sbeet-copper tubing made funnel-shaped. The upper one of these is prolonged into an additional pipe f, by means of which the smoke arrives at the second sack g in the series, thence finding its way to the third, and so on till the last sack of the row is reached. In connection with the last sack of each row is placed a horizontal flue F, in which are arranged frames covered with wire gauze and mounted on hinges. Their purpose is to retain the small remaining portions of lamp-black passing out with the smoke from the sacks. The meshes of the gauze are constantly getting filled up with soot, which neeessitates a periodical ohecking of the draught for its removal. This is done by means of the rod G, which, when raised and allowed to fall suddenly, jerks the accumulated mass off the gauze. The current of air passing through the entire apparatus can be regulated hy a damper placed at the entrance to the chimney in which the flue F emhouches. At regular intervals, the mouthpieces in the lower ends of the sacks are removed, and their contents are shaken out separately and collected according to their various qualities. That gathered from the first sack in each row should always be kept apart from the remainder, as it is much contaminated by the presence of resinous and tarry matters.
A process has been devised by Messrs. Martin and Grafton for the preparation of lamp black from coal-tar, which affords a very good product. The coal-tar is first stirred up ener getically with lime-water in any convenient vessel, after which the mixture is allowed to stand until the coal-tar has subsided to the bottom, when the lime-water is drawn off. The tar is then
well washed by decantation with hot water, and rectified in the ordinary naphtha still. Afterwards it is run into a long iron cylinder, which is placed over a furnace, and supplied with numerous large burners. Each burner has a metal funnel placed immediately above it, connected with a cast-iron pipe, into which all the fumes from each burner are conducted. The naphtha in the cylinder is heated almost to the boiling point by the furnace beneath. A series of smaller pipes lead away the fumes from the main pipe into a row of chambers, and thence into a series of large canvas hags, placed side by side, and connected alternately at top and bottom. The bags vary in number from fifty to eighty, the last one being left open to allow the smoke to escape, after tra versing some 400 yards since leaving the burners. The best quality of lamp-black is found in the last bags, that near the furnace being much coarser and less pure. The bags are emptied when ever they contain a sufficient quantity.
The process employed in Germany for the manufacture of lamp-black is to conduct the products of the combustion of any resinous matter in a furnace into a long flue, at the end of which is placed a loose hood, made of some woollen material, and suspended by a rope and pulley. The lamp-black collects in this hood, and when a sufficient quantity has accumulated is shaken down and removed. In this manner about 6 cwt. of lamp-black may be collected in twenty-four hours.
In England, an inferior variety is sometimes obtained from the flues of coke-ovens. That known as Russian Lamp-black is made by burning chips of resinous deal or pine wood, and collecting the soot formed; hut it is objectionable, owing to its liability to take fire spontaneously when left for a long time moistened with oil.
The lamp-black made in these ways is generally purified hy calcination, in order to remove the empyreumatic oils which it invariably contains. This is effected in close vessels, and the product is called burnt lamp-black, and is especially useful as a water-colour. The particular virtue of lamp black as a pigment lies in its state of extremely fine division, which could not possibly be attained by artificial means ; this quality renders it invaluable as the basis of black pigments, all of which contain it in a greater or less quantity. Indian ink and printers' ink are also composed principally of this substance.
The transport of lamp-black is effected in barrels or bags ; when in the latter, these should be previously soaked in water containing some clay in suspension, which stops up the pores of the sacking, and thereby prevents loss.