Page:Popular Science Monthly Volume 2.djvu/630

610 to be so friable that in a short time the ordinary travel on the streets reduced it to a fine, black powder, which, in dry weather, was thrown up in murky clouds by every passing vehicle and every gust of wind, finding entry into the adjacent houses through the minutest crevices, and in wet weather was kneaded into a nasty, viscous mud. Soon the streets thus paved were impassable, and the commissioners were forced to order the removal of what was left of the "poultice" pavement.

This experience was not well calculated to conciliate public opinion in favor of asphalt as a material for paving; and, though travellers returning home from Paris were loud in praise of the asphalted roadways of that capital, contrasting the roar of our granite-paved, filthy thoroughfares, with the smooth, noiseless, cleanly streets of the French capital, they were listened to with incredulity. Their "odious comparisons," instead of causing us to envy the Parisians for their happy solution of the great question of pavements, had only the effect of exciting compassion for the poor outside barbarians who put their trust in asphalt. For, had we not tried asphalt here, and found it wanting?

Yet it was not the asphalt pavement at all which proved a failure in these experiments. The material used was a spurious compound; a mixture of sand and gas-house refuse, which had this only in common with asphalt, that the two substances went by the same name. Here the adage, "Give a dog a bad name," was reversed. The genuine asphalt pavement was thus involved in the ill-fortune of its base counterfeit; only for a little while, it is to be hoped. So soon as we discover within convenient distance from our centres of population native deposits of asphalt, we shall avail ourselves of the improvements introduced into the art of road-making in France, and the "coming man" can go about his affairs without having his ears stunned by the clatter and roar of vehicles; the horse of the future perform his service without constantly risking life and limb; and the carriage of the future roll along without being jolted to pieces. In France the asphalt pavement is as much a success as the railway, and, as we are still seekers, still experimenters in this matter, it is perhaps well that we learn the processes followed by French engineers.

Dr. L. Meyn, of Halle, has published a pamphlet on "The Asphalts," which sums up all the information that is accessible regarding this material. In the present paper we propose to give, mostly in his own words, the history of asphalt as a material for paving foot-paths and roadways.

Natural asphalt, or asphalt-stone, is a porous, calcareous rock, saturated with bitumen, or natural tar, and capable of being worked into a tough, hard mastic. It is not unlike mortar in general appearance, and its color is usually chocolate, giving a fracture of lighter color. Its grain is fine, and each molecule of limestone is coated with the bitumen. The proportion of the latter in the mass varies from 7 to 15 per cent. At a temperature of between 338° and 356° Fahr.,