Inventions in the Century

by William Henry Doolittle

A more recent improvement consists in the use of pneumatic means for removing the dust that is caused by the use of revolving brooms or brushes, such removal being effected by means of a hood that covers the area of the street beneath the body of the machine, and incloses an air exhaust, the sweepings being drawn through the exhaust mechanism and deposited in a receptacle for the purpose, or in some instances deposited in a furnace carried by the machine and there burned.

In cities having hard, smooth, paved streets and sufficient municipal funds, the most effective, but most expensive way, has been found to keep a large force of men constantly at work with hoes, shovels, brooms, bags and carts, removing the dirt as fast as it accumulates.

Abrading Machines.

One of the most striking inventions of the century is the application of the sand-blast to industrial and artistic purposes.

For ages the sands of the desert and wild mountain plains, lifted and driven by the whirling winds, had sheared and polished the edges and faces of rocks, and cut them into fantastic shapes, and the sands of the shore, tossed by the winds of the sea, had long scratched and bleared the windows of the fisherman’s hut, before it occurred to the mind of man that here were a force and an agent which could be harnessed into his service.

It was due finally to the inventive genius of B. F. Tilghman of Philadelphia, Pa., who, in 1870, patented a process by which common sand, powdered quartz, emery, or other comminuted sharp cutting material, may be blown or driven with such force upon the surface of the hardest materials, as to cut, clean, engrave, and otherwise abrade them, in the most wonderful and satisfactory manner.

Diamonds are abraded; glass depolished, or engraved, or bored; metal castings cleaned; lithographic zinc plates grained; silverware frosted; stone and glass for jewelry shaped and figured; the inscriptions and ornaments of monuments and tombstones cut thereon; engravings and photographs copied; steel files cleaned and sharpened, and stones and marble carved into forms of beauty with more exactness and in far less time than by the chisel of the artisan.

The gist of the process is the employment of a jet of sand or other hard abrading material, driven at a high velocity by a blast of air or steam, under a certain pressure, in accordance with the character of the work to be done. The sand is placed in a box-like receptacle into which the air or steam is forced, and the sand flowing into the same chamber is driven through a narrow slit or slits in the form of a thin sheet, directly on to the object to be abraded.

By one method the surface of the object is first coated with tinfoil on which the artist traces his design, and this is then coated with melted transparent wax. Then when the wax is hardened it is cut away along the lines already indicated, and seen through the wax. The object now is subjected to the blast, and as the sand will not penetrate a softened material sufficient to abrade a surface beneath, the exposed portions alone will be cut away. The sand after it strikes is carried off by a blast to some receptacle, from which it is returned to its former place for further use. Other means may be used in the place of a slitted box, as a small or larger blow-pipe; but the driving of the sand, or similar abrading material, with great force by the steam or air blast, is the essential feature of the process.

Emery, that variety of the mineral corundum, consisting of crystalline alumina, resembling in appearance dark, fine-grained iron ore, ranking next to the diamond in hardness, and a sister of the sapphire and the ruby, has long been used as an abradant. The Eastern nations have used corundum for this purpose for ages. Turkey and Greece once had a monopoly of it. Knight says: “The corundum stone used by the Hindoos and Chinese is composed of corundum powdered, two parts; lac resin, one part. The two are intimately mixed in an earthen vessel, kneaded and flattened, shaped and polished. A hole in the stone for the axis is made by a heated copper rod.”