An especially fine quality of lamp-black is obtained from bone-oil, deprived of the ammonia with which it is always contaminated. It is manufactured on a commercial scale by means of the apparatus shown in Figs. [3] and [4]. 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 farther 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 surrounds 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 feet, as indicated in the figures. The effect of this wide tube c is not only to cool the smoke, 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 feet long and 3 feet in diameter, closed at the bottom with a trap or slide e, and formed at the upper and lower ends of sheet-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 necessitates a periodical checking 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 by a damper placed at the entrance to the chimney in which the flue F embouches. 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.
Fig. 5.—Apparatus for making Lamp-black.
The old-fashioned method of preparing lamp-black from the incomplete combustion of gas tar is conducted in an apparatus resembling that shown in [Fig. 5]. The furnace a, lined with fire-brick, contains a kettle b, and is surmounted by a large thick cast-iron hood c, communicating with a stone or brick condensing chamber, divided by means of perforated partition walls into three unequal sized compartments d, e, f, wherein the black is deposited. A chimney g delivers uncondensed vapours into the atmosphere. In working, the furnace is first brought to a red heat, then the kettle b, charged with tar, is introduced. As a charge is finished, more tar is added, with occasional stirring, till the kettle becomes inconveniently full of residue, when it is withdrawn and a fresh one replaces it. The residue is chipped out and used as fuel. The black is removed weekly through the door h. It is of good quality and colour so long as the combustion is conducted with a minimum of air, admission of which is controlled at the furnace. The yield is about 25 per cent. of the weight of the tar; and one furnace should treat a ton of tar in a week. One workman can manage several furnaces.
An improved process has been introduced by 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 energetically 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 bags, 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 traversing 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 whenever 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.
One form of the apparatus is shown in [Fig. 6]. The circular structure a is lined inside with hanging cloths upon which the black can condense, and is covered with a conical roof from which depends a movable sheet-iron cone b, perforated at its apex to give egress to a current of air. This cone b is supported by a rope g passing over a pulley c and accessible from the outside. A fireplace d, containing a small iron dish e for holding the resin, is built against one of the side walls of the structure in such a manner that it can be fired externally. The rate of combustion is regulated by a small sliding damper on the door of the fireplace. When the black has accumulated in the chamber a to such an extent that operations must be suspended, the fire is let out, and the chamber is left to cool entirely, so that the black may not ignite on contact with the air. The cone b is then lowered, and in its descent scrapes the walls of the chamber a and causes the black to collect on the floor, whence it is removed through an iron door f which at other times is kept tightly luted.
