Page:Popular Science Monthly Volume 61.djvu/223

Rh than 20 years old. and in fairly good condition. A better imitation, or what was supposed to be a better one, was made of pitch from the celebrated pitch lake of Trinidad and the liquid residuum of the petroleum stills, which was then a drug on the market.' This mixture was tempered with sufficient sand to make about 90 per cent. of the mineral matter and laid, spread and rolled like the European asphalt. The experiment proving a success, the name 'asphalt street' was applied to these artificial imitations of asphalt. No harm came from this wrong application of M. Malo's word for many years, as the use of it was confined to street surfaces of which natural bitumen was the principal constituent.

About 1890, the late Joseph D. Weeks, of Pittsburg, visited the Pacific Coast and found that the petroleum refiners of California were making a solid residuum from the distillation of petroleum and calling it 'asphalt.' Mr. Weeks immediately conceived the idea that California petroleum contained 'an asphaltic base,' or in other words, it might be considered to be asphaltum dissolved in petroleum from which it could be separated by distilling off the petroleum. This very erroneous conclusion led to a second one, viz., that the residuum of the distillation of California petroleum is practically the same thing as natural asphaltum. On the contrary, these residuums of petroleum, no matter in what manner they may be made, are the product of destructive distillation and should be made the subject of prolonged and careful experiment before they are used in any considerable quantity as an equivalent for natural asphaltum.

The difficulty which M. Malo feared would follow the careless use of terms to designate the different forms of bitumen has overtaken us, inasmuch as the word 'asphalt' is now applied to a large number of the most heterogeneous substances, quite unlike in many respects, but having other properties, denominated bituminous, in common.

An enumeration of these materials will illustrate my meaning. The natural solid bitumens are M. Malo's asphalts, called in the United States rock asphalt, and including bituminous sandstones, as veil as limestones, of which there are large deposits in California, the Indian Territory and Kentucky; Trinidad pitch; Bermudez, Cuban, California, Mexican and other asphaltums; Gilsonite, the bituminous coquina or shell limestone of Uvalde County, Texas, with the extracted bitumens of California and the Indian Territory. All these materials have been used successfully in making asphalt surfaced streets.

The so-called artificial asphalts, called asphalts by local application of the word, are the solid residuums of the so-called asphaltic petroleum, found in California and Texas; Pittsburg Flux, which is the residuum made by burning out the hydrogen from petroleum with sulphur; residuums made by several other patented methods and sold under various