Page:Popular Science Monthly Volume 22.djvu/201

Rh in West Virginia and other parts of the country. In the mountains west of Denver, in Colorado, is a vertical bed of hard and brittle asphalt, not unlike Grahamite, while Albertite is found in small quantities in Lorain County, Ohio, and Casey County, Kentucky.

Bitumen is likewise found in Cuba, and is brought into commerce under the name of chapopote, or Mexican asphalt.

In Europe asphalt occurs chiefly in limestone, which forms, when crushed and packed, an excellent pavement. The principal points at which it is found are the following: Val de Travers, in the Swiss Canton of Neufchâtel, fourteen miles from Neufchâtel, and sixteen or seventeen miles by rail from the French borders; Seyssel, on the Rhône, in the French department of the Ain, about thirty-three miles from Geneva; Lobsann, a small town in northern Alsace; Vorwohle, in Braunschweig; and Limmer, near the city of Hanover. The Italian province of Caserta, in the neighborhood of Naples, supplies Rome with an asphalt much used for terraces and flat roofs.

The quantity of bitumen in these limestones and the manner of its dissemination are quite varied, but it is generally found that the softer limestones contain more bitumen than those which are harder. The average amount is about ten per cent, but it sometimes reaches twenty or thirty per cent, and occasionally there are cavities in the rock which are filled with bitumen. At other times the quantity sinks to five per cent, or less, while nodules of limestone entirely free from it are also found. The value of the rock depends on the percentage of bitumen, and on other circumstances. If the stone is to be used for making mastic, the higher the percentage the more valuable it is; but, if used directly for paving, a uniform distribution, not exceeding eight or ten per cent, is desirable.

Asphalt-stone, to which Malo limits the name of asphaltum, varies in color from gray to brownish-black, according to the richness in bitumen; that of medium quality closely resembles chocolate in color. That which is poor in bitumen is hard, and rings like ordinary limestone; but the fatter rock, when struck with a hammer, gives forth a dull thud, like a block of wet plaster, and takes an impression from the blow. If it contains more than ten per cent, it crumbles in the hand, and can be cut with a knife, like chocolate. Good stone, with about ten per cent of bitumen, has a specific gravity of 2·1. Some asphalt-stone is of a spongy, hygroscopic nature, and consequently lighter.

One peculiarity of the natural rock-asphalt is that, when heated over a fire, it breaks up into a brown powder, and then, at a higher temperature, all the bitumen is expelled, leaving a pure white powder. An unsuccessful attempt was made in the Paris Conservatoire des Arts et Métiers to imitate this asphalt-stone by forcing thick, pasty bitumen into pure limestone by great pressure. When, however, the lime-stone was boiled for a long time in a liquid mass of asphalt, it