View of Zinc Oxide Fume Pipes with electrically driven Suction Fans] The color of the pigment is largely due to the carbon and the lead sulphide. Its specific gravity is 6.4, and it grinds in 10% of oil to a stiff paste, 100 lbs. of which may be thinned with about 26 lbs. of oil to working consistency. Paint manufacturers use it in mixture with iron oxide and other pigments for the production of paints for metal surfaces. Wood and others have found it of great value for this purpose. It has a tendency to chalk, but this may be overcome by admixture with other pigments such as zinc oxide and iron oxide. Lane has found it to be very durable when admixed with lampblack. [Illustration: View of Bag Room receiving Zinc Oxide] =Zinc Oxide.= This extremely white and fine pigment is prepared by the roasting and sublimation of franklinite, zincite, and other zinc-bearing ores largely found in New Jersey. Its purity approaches in most instances 99.5 or more. It has a specific gravity of 5.2. On account of its stability, whiteness, and opacity, it is invaluable as a pigment when a constituent in a combination formula. Its extreme hardness renders it less resistant to temperature changes, when used alone. Under the microscope the fineness and structure of the particles are clearly evident. The French-process zinc oxide produced in America by the sublimation and oxidation of spelter is the purest made, and superior to imported grades which often contain ultramarine blue as a whitening agent. [Illustration: Zinc Oxide] [Illustration: Zinc Lead White] [Illustration: Zinc Lead. By transmitted light (_The Pigment shows black_)] [Illustration: Lithopone] [Illustration: Magnesium Silicate (Asbestine)] =Zinc Lead White.= This extremely fine pigment, consisting of about equal parts of zinc oxide and lead sulphate, results from the reduction, volatilization and subsequent oxidation of sulphur-bearing lead and zinc ores. It has a specific gravity of 4.4. Its slightly yellowish tint bars it from being used alone very extensively, but when mixed with white lead, zinc oxide and inert pigments, or used as a base for colored paints, it is of considerable value. The magnification of the particles shows the peculiar way in which the pigment agglomerates, and the characteristics of a fine, uniform pigment. [Illustration: Asbestine Mine at Easton, Pa.] [Illustration: American Barytes. Transmitted light (_The Pigment shows black_)] [Illustration: German Barytes. Mag. 250 Diam. (_The Pigment shows white_)]