Page:Popular Science Monthly Volume 7.djvu/94

84 in the show-windows, and haunting the anxious housewife in kitchen, pantry, and cellar. The devoted denizen finds but a partial protection against the shocking nuisance, when he mixes this dust with an abundance of water—by sprinkling the street.

A modification of the macadam is the Telford road; it consists of a bed of firmly-wedged quarry-stones, with an even surface as a foundation, upon which a layer of larger and a layer of smaller broken stone, mostly trap-rock, are spread, each being rolled by horse and steam rollers. Upon the well-compacted surface a binding of screened gravel is applied, moistened and rolled in, so as to present one solid mass, which, while hard and durable, yet retains some elasticity. This variety, superior for country-roads, though still open to the vital objection of dust, is equal in price to the costly modern city pavements, and therefore has found but a limited application within city limits—for instance, on the Boulevards of New York.

Wood pavements which, at one time, were much used in Britain, especially in London, and also in New York in 1835 and 1836, but were abandoned for weighty reasons, and especially on account of their rapid decay, were revived in the rising cities of the great West, notably Chicago, where stone was scarce, lumber was cheap, and a porous, sandy subsoil retarded the decay of the perishable woodblocks by dry rot from below, as happens on retentive soil. These wood pavements, smooth, noiseless, and advantageous for traction, were rather hastily adopted by municipal committees or boards in Eastern cities, where the conditions were different, and where decomposition commenced after two or three years' use. The heavy profits made induced a desperate fight in their favor by interested parties, a renewed effort in behalf of "treated" wood gave them a respite and a second harvest before final disuse, which was accelerated, however, by the overwhelming complaints of the offensive and unhealthy effluvia emitted from them; so that, in a sanitary point of view, the advantage of the absence of stone-dust was much overbalanced by the decomposition of the material itself.

The wood-blocks during treatment have been mostly impregnated, by pneumatic processes, with chloride of zinc, sulphate of iron, or oily, creosotic substances; and, though railroad-sleepers, telegraph-poles, etc., have been satisfactorily preserved through these agencies, such methods have failed, for various causes, to render an equivalent for the expenses incurred in treating the paving-blocks. But the patience of the people is not yet exhausted, and, in Northwestern cities, a new and costly revival is being arranged by the substitution of sulphate of copper for impregnation, a substance used in France, under M. Boucherie's patent, for thirty-five years past. The District of Columbia has been preëminently the experimental ground for treated wood pavements. An investment of about $5,000,000, a sum far in excess of that in any other city of the globe, has been made there within