Page:Popular Science Monthly Volume 22.djvu/203

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pressed asphalt pavements, or converted into "mastic" by mixing it with one tenth to one seventh its weight of purified bitumen from Trinidad and cooking five or six hours. It is then poured into cast iron molds without bottoms, which are placed on the sanded floor of the shop. These blocks of mastic are fifteen inches in diameter and four inches thick, weighing fifty or sixty pounds each. Those made at Val de Travers are hexagonal in form, bearing a trade-mark of a cross and vt; those from Seyssel and Lobsann circular; the others oblong, with rounded corners.

The Val de TraVers mastic and asphalt rock are imported by the Neufchatel Asphalt Company (54 Astor House, New York); the Seyssel mastic by the New York Mastic Works (35 Broadway); the Limmer and Vorwohle rock asphalt by C. Wichtendahl (111 Broadway, room 97). In regard to their uses in this city we shall speak more fully in another place.

Trinidad asphalt is imported and refined by the Warren Chemical and Manufacturing Company (45 John Street). This substance, as it occurs in nature, is very impure; about one third of the mass consists of water, another third is made up of clay and sand, so that only one third is actually bitumen. It is melted in large kettles and heated for twelve hours to expel the water, the earthy constituents settling to the bottom. This partially purified asphalt, which still contains about twenty per cent of impurities, is poured through a sieve into barrels, where it solidifies. It now forms a brittle mass, which sells for twenty-five dollars per ton. It is too hard for mixing with the pulverized asphalt-rock, or for street pavements. At Val de Travers and Seyssel the residues from the distillation of bituminous shale, known as "shalegrease," are used to soften it, while in other places similar residues of paraffine manufacture or petroleum refining are added to the natural bitumen to form what is known as "prepared bitumen," or mineral tar. In this country the so-called "still-bottoms" from petroleum-stills are used in the proportion of fifteen parts of the latter to eighty-five of the natural asphalt; the portions may be varied to suit the climate and other conditions.

Asphalt pavements may be divided into three classes. The first, which is commonly known as mastic (asphalte coulé), is best adapted to sidewalks, court-yards, and other places where there is but little heavy traffic. It is prepared by melting the blocks of mastic, already described, in caldrons, adding a small quantity of prepared bitumen, and afterward stirring in thirty or forty per cent of clear grit. When thoroughly mixed it is carried to the spot in pails, and spread with a wooden float by a skilled workman on his knees. It is then rubbed until perfectly smooth, and fine sand strewed over it. Examples of this pavement can be seen in Union Square, Tompkins Square, and several other places in New York city.

Compressed asphalt is better adapted to heavy traffic, as in street