Aside from such of the rock asphalt as is used for paving, most of the asphalt of com merce is a relined product. or else the latter made into either asphaltic cement or mastic. Asphaltic cement is refined asphalt, tempered with residuum petroleum oil, maltha, or some other material, but generally the oil. From 15 to IS pounds of oil is added to 100 pounds of refined asphalt, the amount of oil varying with the uses to which the cement is to be put. The two ingredients are mixed while hot, being agi tated by mechanical means or by air. Mastic is prepared from crushed or powdered rock asphalts, and also from relined asphalt. Either asphaltic cement or maltha is used with the rock asicha It, and sand and perhaps powdered limestone with the cement. The mix ture is made tinder heat, and is run into molds for shipment. When used for floors, sidewalks, or fools, the mastic blocks or cakes are melted, refined asphalt and sand or tine gravel are added in small quantities, until the desired consistency is attained. Powdered limestone
may be used in place of gravel or sand, par ticularly where a hard, dense, impervious final product is desired. Asphalt concrete is simply crushed stone or gravel bound together with mastic, the two mixed hot and compressed after being put in place. Some Of the most impor tant uses to which asphalt is put are for pave ments. pipe coatings, and reservoir linings. See PAVEMENTS; DAMS AND RESERVOIRS.
BIBLIOGRAPHY. For further information on Bibliography. For further information on mining and refining, consult: Tillson, Pave ments and Paring Materials (New York, 1900) ; J. W. Howard, Natural Asphaltum. and Its Compounds (Troy, N. V., 1894) ; The Mineral Industry, Vol. VII. (New York. 1898) ; Henry, "Some Facts Relating to the Asphalt Paving Industry" (originally in The Polytechnic, Tray, N. Y.: also abstracted in Engineering Selys, New York, March 4, 1900). See ASPHALTIC COAL ; BITUMEN ; BITUMINOUS LIMESTONE ; BITU MINOUS SANDSTONE; PETROLEUM.