Page:Popular Science Monthly Volume 2.djvu/631

Rh falls to powder, and may then be dissolved in hot melted bitumen.

This substance does not occur very abundantly in Nature, the only deposits of any importance, so far as yet known, being found in the Val de Travers and at Seyssel, in Switzerland; Seefeld, in the Tyrol; Lobsan, in Alsace; Hölle, in Holstein; and Limmer, in Hanover. The deposit at Hölle is by far the most extensive in Europe; but, though here the particles of the limestone are thoroughly permeated by the bitumen, the material is not considered by the Paris Asphalt Company to be suitable for pavements, because it contains an excess of pure petroleum. Yet Dr. Meyn thinks that by exposure to air the greater part of this surplus may be dissipated, and the remainder oxidized.

Ancient authors state that Babylon was partly built with asphalt, and that an asphalt cement was used for the walls of Nineveh. A Greek physician, Eirinus, endeavored to bring this substance into use as a building material in 1712. He was the first to discover a method of reducing the asphalt of the Val de Travers to the liquid state, and obtained the monopoly from the King of Prussia of all the asphalt beds he might discover in the principality of Neufchâtel. He published in 1721 a "Dissertation on Asphalt," in which he gives as follows the process of making asphalt cement: "The preparation of this cement is very easy. The stone must be slightly warmed till it can be coarsely powdered. A small quantity of pitch is added, to make it thinner and more soluble, and then the whole is melted over a slow charcoal-fire." This cement was to be used instead of mortar, and also to protect wood and stone-work against decay. There is still to be seen at Couvet, a little village in the Val de Travers, a flight of stone steps, dating from the time of Eirinus; the lower steps are coated with asphalt, and are almost entirely unimpaired, while the upper ones, which were not so protected, are worn into holes. But the material did not continue long in use for building purposes, for in 1802, after the discovery of asphalt-stone at Seyssel, near Geneva, we find the preparation of a mastic, from bituminous limestone and tar, heralded as a new invention.

In 1832, the Seyssel quarries fell into new hands, and from that period we date the progress made in the matter of asphalt pavements. The new proprietor of the quarries, Count Sassenay, devoted himself exclusively to producing a continuous and homogeneous material, and carefully instructed his workmen in the best manner of laying this pavement. The celebrated foot-path of the Pont Royal, the fine pavement of the Place de la Concorde, Paris, as well as many pavements at Lyons, belong to that period. Sassenay's process is still employed in preparing asphalt for paving foot-paths, and the mode of laying down the pavement is as follows: The foundation must be even, for any inequality of its surface will cause the pavement to wear out more rapidly in some parts than in others. The mastic is broken into