In 1914 there were in the United States 44 plants for the manufacture of artificial asphalt. The following table shows the output and value of the artificial product, made from domestic material, since 1909: Short Tons Value moo 129.594 $1.565.000 1910 161,187 2,225,000 1911 277,192 3,173.000 1912 3.755,000 1913 360.653 3.013,000 191$ 1916 0078.851 Recent analyses of true Barbados asphalt and of the artificial have given the following results: Specific gravity, natural, 1.0143; arti ficial, 1.393. Hardness according to Mobs, nat ural, one to two degrees M. ; artificial, two to three degrees M. Hardness according to Breit haupt, natural, one to two degrees B.; artificial, three degrees B. Soluble in petroleum, natural, very easily; artificial, with great difficulty, slowly and incompletely. Soluble in benzine, natural, very easily and completely; artificial, with great difficulty, slowly and incompletely. Soluble in benzol, natural, very easily and com pletely; artificial, rather easily. Solubility in wax, natural, not known; artificial, in five to six days, leaving an amber-like remainder. The solution in benzine of the Barbados natural as phalt gives a beautiful brownish varnish layer. which dries in about 10 minutes; that of the artificial asphalt, however, does not ; therefore, the first is to be preferred for fine varnish.
Uses of Asphalt— The purest varieties of asphalt are used to a great extent in the manu facture of asphalt varnish. A' refined asphalt usually mixed with some petroleum residuum is used for saturating felt; machinery is used in the process, and a paint or varnish of similar composition is usually applied after the asphalt felt is in place. Asphalt felting has an advan tage over coal-tar felting in that it is not ren dered brittle by heat or with age. Insulating
paints are made from extracted bitumens of asphalt admixed with various substances, so as to produce a hard product corresponding to ebonite. The most important application of asphalt is in the paving industry, in which two methods are employed; asphalt block paving, in which blocks of asphalt composition are first manufactured by machinery, and sheet asphalt, in which the asphalt composition is spread and rolled so as to form large continuous sheets. Upward of 3,000,000 square yards of such pave ments were laid in the principal cities of the United States in 1916. The consumption of as phalt and asphaltic materials in the United States is rapidly increasing, amounting in 1916 to 1,456,634 short tons — as compared with 1,224,037 short tons in 1915, and 851,699 short tons in 1914. Besides the domestic consump tion, the United States manufactured and ex ported in 1916 asphaltic articles amounting in value to $494,895, in addition to an export of 36,443 tons of crude asphalt; the entire export trade being valued at $1,254,664.
Bibliography.— Klein and Peckham, 'As phalt Paving' (Report of the Commissioners of Accounts of the City of New York 1904) ; Kohler,• 'Die Chemie und Technologie der rtatfirliche und kiinstliche Asphalt& (Braun schweig 1904) ; Richardson, 'Modern Asphalt Pavement' (New York 1905; 2d ed., 1998); and 'Asphalt Construction for Pavements and Highways' (New York 1913) ; Eldridge, 'The Asphalt and Bituminous Rock Deposits of the United States' (in 22d annual report of the United States Geological Survey, pt. 1, Wash ington 1901). See MINERAL PRODUCTION OF THE UNITED STATES.