AS'PHALT, or ASPHALTUM (Gk. 'Ad -op, asphaltos, -on. a loan-word of un certain origin). A bituminous substance of solid consistency occurring in nature and be longing to the same series of hydroearbon com pounds as petroleum and natural gas. It is also called Jews' pitch, Dead Sea hitmnen, com pact bitumen, and Trinidad bitumen. Asphalt probably owes its origin to vegetable matter which has been subjected to a slow process of decay, the hydrocarbon compounds having dis tilled off and settled in neighboring deposits. It is in fact produced artificially in the manufac ture of eoal-gas, in which process much tarry matter is evolved from the retort. If this tar be subjected to partial distillation, naphtha and other volatile matters escape, while artificial asphalt is left behind. Asphalt commonly has a pitchy odor, a black or dark-brown color. but does not soil the fingers: it is insoluble in water, sparingly soluble in alcohol, but is dis solved in greater part by ether, oil of turpentine, and naphtha. Its specific gravity ranges from 1 to 11. and it burns readily with a smoky flame. In nature, asphalt occurs in sheets or lakes, mixed with earth, as in Trinidad and Venezuela, or mixed with sand, or in sandstone. or in limestone (asphaltic or bituminous lime stone), as is the case in Cuba, California, and Utah.
The largest natural deposit of asphalt is on the island of Trinidad, where the so-called Pitch Lake exists. This is a great basin-shaped deposit of asphalt, 18 feet deep near the margin, and 78 feet in the centre, and although solid in ap pearance, there is nevertheless a continual but almost imperceptible motion throughout the mass. The surface of the lake is 148 feet above sea level, and from the edge several streams of as phalt have flowed dolvr the slope toward the shore. Excavations made to a depth of 20 feet
have filled lip again in f, months. While the as phalt is solid enough to drive a wagon and team across it, still the slow movement of the ma terial tends to draw in the tracks laid out to the pits. unless properly supported. Another asphalt lake occurs in Venezuela, and the prod uct is known as Bermudez asphalt. It is a swampy tract of about 1000 acres, in which there are numerous pitch pools supplied by springs. Asphalt is also found on the shores of the Dead Sea in large quantity and is known to the Arabs by the name of Hajar mousa, or Moses's stone; while a fluid form occurring in California is known as maltha. or mineral tar. The occurrence of asphalt is not restricted to any one geological formation, but it is not known in the Arch:can. The deposits of asphalt in the United States are insufficient to meet:the demand, and large quantities are imported. chiefly from Trinidad and Venezuela.
The uses of asphalt are numerous. It is em ployed as an ingredient of varnish and also as an insulating material. Buildings and other objects arc often coated with it, to protect them from dampness, and vessels are painted with asphalt to protect them from the 'Pert-do, or ship-boring worm. Asphalt alone is not used for medicine, lint its natural solution in naphtha —viz. petrolcum—is of medicinal value. used either internally or externally. Alaiut 1840 asphalt became of importance as a material for paving, and for this purpose it was mixed with powdered rock when hot, and then spread on the surface to he paved. Asphalt pavements are smooth and clean, but less durable than stone, and in moist climates are often slippery.