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Location of Mines

asphalt, lake, matter, surface, water and land

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LOCATION OF MINES Asphalt is found mixed with more or less earthy and vegetable matter, or impregnating limestone or sandstone. The localities where it is found are shown in Table 39. "One or more mines are worked in each of these countries, except, perhaps, Columbia, Indian Territory. Montana, New Mexico, Mich igan, Washington, and Dalmatia." The principal sources of supply will be considered separately.

Trinidad Asphalt.

The Island of Trinidad near the north east coast of Venezuela, South America, supplied something like 90 per cent of all the asphalt used in the world from about 1875 to 1900. At present the Island of Trinidad is the main source of supply of the asphalt used in the United States.

The island contain about 1,750 square miles.t Near the south west corner is the so-called pitch-lake, which has an area of about 115 acres. The surface of the lake has an elevation of 138 feet above the sea-level, and the asphalt has a depth of 78 feet near the center. The surface of the lake has a slight fall from the center toward the sides, and a general inclination toward one side, and is covered with irregular flattened domes, separated by channels of flowing water a few feet wide and a few inches deep. There are several islands 50 to 60 feet in diameter scattered over the surface of the lake, which have sufficient depth of soil to support the growth of large trees. The surface of the asphalt is sufficiently hard that teams may be driven over it; but the whole mass is in constant motion around several vortices, as shown by trunks of trees which rise and after a time disappear again. Excavations made during the day close up during the night. At a place in the center, called the boiling spring, soft pitch wells up, but soon becomes hard. The appearance of boiling is due to the escape of large volumes of sulphuretted hydro gen.

The asphalt is excavated with picks and shovels, conveyed to the shore in carts, and lightered to vessels off-shore. On the voyage it becomes compacted into a solid mass and must be again broken up with picks. The crude asphalt is mixed with much earthy and

a little vegetable matter and water and is dark brown, brittle, and as dense as dry peat.

The crude material is refined by placing it in kettles or open tanks and heating it for three or four days, during which time the water is evaporated, the vegetable matter rises to the surface and is skimmed off, and the earthy material settles to the bottom. Although this is called refining, it is really little more than a drying process, since but little mineral matter subsides, and only the water and the volatile oils are driven off. The mineral matter, if inert and insoluble in water, is not detrimental to an asphalt for paving purposes; but the non-bituminous organic matter and the soluble mineral matter are prejudicial. Great care is required in the refin ing process not to heat the asphalt to a point where chemical changes take place. The refined asphalt must be softened by the addition of some fluxing material before it is ready for use in the pavement The above refers to asphalt obtained from the so-called lake; but asphalt is also mined from the slopes between the lake and the sea. The former is called lake asphalt, and the latter land or overflow asphalt, or less frequently iron pitch. Both have the same origin, the land asphalt simply being asphalt from the lake which has overflowed the surrounding land. The land asphalt, having been exposed to the elements for a longer time than the lake asphalt, and having lost part of its volatile oils and having been partially oxidized, is less plastic than that from the lake. For a number of years there was a sharp commercial controversy as to the alleged superiority of the lake asphalt; but at present the controversy has practically subsided. The composition of neither is uniform, and therefore the above difference is not of much im portance, particularly as only about 10 or 12 per cent of the asphalt mixture in the pavement is asphalt. The average composition of the three grades is shown in Table 40.

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