For manufacturing lamp-black, a slow rotary motion is imparted to the apparatus by means of the worm and worm-wheel, and a slight current of water is directed upon the plate A through the pipe _g_. The lamps J, filled with paraffin oil derived from lignite, or with any other suitable oil, are ignited and approached to the plate A as far as is necessary for cooling the flame, so as to deposit the greatest possible quantity of black. The latter adheres to the cold surface of the plate, which is also kept damp by the aqueous vapour formed during the combustion. The revolution of the plate serves to bring the flame continually into contact with new and clean portions of the plate, the black being continually scraped off by the blade or scraper placed opposite the flames, and conducted through a channel into a collecting trough. There is a risk of overburning, causing a grey tint and a hard and granular texture. A variety of lamp-black known as “carbon black” or “gas black,” has of late years assumed an important position among black pigments. It is produced in considerable quantities in the United States by the combustion of the natural gas issuing from the earth in the mineral oil regions. The soot arising from the imperfect combustion of the gaseous hydrocarbon is made to deposit itself on cooled iron surfaces. These at first were made stationary, but now take the form of revolving discs or cylinders, which are automatically cleansed of the black as fast as it is deposited. This type of lamp-black is remarkably free from mineral impurities and unburned oil, and of a full colour. An improved lamp-black kiln has been introduced in which the use of water is dispensed with. It is shown in Figs. 9 and 10. The furnace A, which is preferably built double, as shown, is constructed of brick lined with firebrick, with a rear wall _a_ that divides the furnace room from the condensing room, side walls _b_, front _c_, and central dividing wall _d_, that divides the furnace into two long and narrow fire [Illustration: Figs. 9 and 10.--AMERICAN LAMP-BLACK KILN.]