In producing the various grades of lampblack, soot oil, which is the last oil obtained in the distillation of coal tar freed from naphthaline as far as possible, is burned in a special furnace. In this furnace is an iron plate, which must always be kept glowing, and upon this plate the soot oil trickles from a vessel fixed above. It is decomposed, and the smoke (soot) rises into four chambers through small apertures. When the quantity of oil destined for decomposition has been used up, the furnace is allowed to stand undisturbed for a few days, and only after this time has elapsed are the chambers opened. In the fourth chamber is the very finest lampblack for lithographers' use; in the third is the fine grade employed in making printers' ink; while the first and second contain the coarser soot, which, well sifted, is sold as flame lampblack. From grade No. 1 the calcined lampblack for papermakers is produced. For preparing this lampblack, iron capsules with closing lids are packed tightly with the coarse lampblack, and the cover is smeared with fine loam. The capsules are next placed in a stove and semi-calcined, this causing the oils to evaporate and the remaining lampblack to become odourless.

The capsules are allowed to cool for a few days before being opened, as the soot dries very slowly, and easily ignites in contact with air if the capsules are opened too soon. For the purpose of preparing completely calcined lampblack, the semi-calcined substance is packed into fresh capsules, these being closed up well. After a calcination lasting two days, the capsules are opened, and the lampblack, which is found to be in compact pieces, removed.

For the manufacture of soot black another furnace i- employed. Asphalt or pitch is thrown in through the doors, air being excluded as far as practicable, and the smoke escapes through the chimney to the soot chambers 1, 2,3,4, and 5, and in these chambers the soot assorts itself. The asphalt or pitch is burned up completely, and the furnace is then left unopened lor several days; then the outside doors are slowly opened and air is admitted. Later on the doors can be opened altogether, if the soot black is quite cool. Chamber I contains the finest soot black, and this is used in the manufacture of leather-cloth and oilcloth. In the other chambers is fine and ordinary flame black, which is sifted and packed in suitable barrels. Calcined lampblack may also be produced from it, the operation being the same as for oil black.