Thirty miles from Cleveland, at North Amherst, Ohio, is the largest sandstone quarry in the world. Its owners, the Cleveland Stone Company, in their original plant employed steam from no fewer than forty-nine boilers, all machinery, including drills and channelers, being driven by steam. In January, 1904, this was replaced by a centralized air plant which has resulted in marked economy. In the power-house four water-tube boilers, each of 257 horse-power rated capacity, drive compound compressors which deliver air at about 100 pounds pressure. This air, duly piped, is distributed to drills, channelers, hoists, pumps, saws, grindstones, forge fires, and so on. Economies, familiar in electrical centralization, are here paralleled in an interesting way. In the working day not a moment is wasted. When the whistle blows the full working pressure is ready to begin work and maintain duty until night. There is no fluctuation of pressure due to careless boiler attendance; no wheeling coal or water barrels to keep pace with advancing channelers. Some of the old boilers, discarded from steam service, are used as air receivers, these and other reservoirs, together with the pipe line itself, unite their immense storage capacity so that throughout the day there is no peak load. Incidentally the new plant renders the quarry free from smoke-laden steam such as of old darkened its air and soiled its output. Fuel and labor under this system were reduced one half when a month of the old service was compared with a month of the new. In one case steam is used for power outside of the main plant. Close to the power-house is a mill where eleven gang saws are driven by a steam engine of 175 horse-power. The nearness of this engine to the boilers ensures a somewhat higher economy than if compressed air were employed. Here, as everywhere else, the engineer engages whatever servant will do good work at the lowest wages.
Westinghouse Air Brakes and Signals.
By all odds the most important use of compressed air is that developed by Mr. George Westinghouse, of Pittsburg, in his automatic brakes for railroads. For each locomotive he provides an air compressor which fills in the engine itself, and beneath each car, a reservoir of compressed air. Every reservoir aboard a long train in rapid motion may at the same instant, by a touch from the engine-runner, actuate the brakes so as to stop the train in the shortest possible time. This invention has accomplished more for the safety of quick railroad travel than any other device; no wonder, then, that Westinghouse brakes are in all but universal use. They are now being adopted for trolley-cars which often require to be stopped in the briefest possible period. The Westinghouse Company builds and installs elaborate signal systems worked by compressed air and electricity. All these are described and pictured in the “Air Brake Catechism,” by Robert H. Blackall, published by N. W. Henley & Co., New York. This book is constantly appearing in new editions, of which the reader should procure the latest.
CHAPTER XXIX
CONCRETE AND ITS REINFORCEMENT
Pouring and ramming are easier and cheaper than cutting and carving . . . Concrete for dwellings ensures comfort and safety from fire . . . Strengthened with steel it builds warehouses, factories and bridges of new excellence.
Stone and wood in the builder’s hands require skill and severe labor for their shaping; vastly simpler and easier is the task of molding a wall from wet clay, or other semi-plastic material. It was long ago discovered that certain mixtures of clay and sand, duly mingled and burned, became as hard as stone. To this discovery we owe, among other arts, that of brick-making. In joining brick to brick, or stone to stone, a mortar of uncommon strength was used by the Romans. All by itself, when laid a little at a time, it formed a strong and lasting structure. Then it occurred to some inventive builder, Why not save mortar by throwing into it gravel and bits of broken stone? He accordingly reared a wall of what we should now call rude concrete, whose lineal descendant to-day is a semi-plastic mass of Portland cement, sand, and gravel or broken stone, together with the necessary water. Its use allows the ease and freedom of pouring, while affording structures with all the strength of stone or brick.
For much of the early work lime and sand were mixed to make a mortar of the usual kind, in which stone or gravel was embedded. Afterward it was found that volcanic ashes, such as those of Puzzuoli near Naples, formed with lime a compound which resisted water and was therefore suitable for structures exposed to damp or wet. In the middle ages concrete was employed throughout Europe, after the Roman fashion, for both foundations and walls. In walls it was usually laid as a core faced with stone masonry, large stones often being embedded in the mass. About 1750, while building the third Eddystone Lighthouse, John Smeaton discovered that a limestone which contained clay, when duly burnt, cooled, ground, and wetted, hardened under water, was indeed a natural cement, by which name it is still known. Deposits suitable for the direct manufacture of natural cement were in 1818 discovered in Madison and Onondaga Counties, New York, by Canvass White, an engineer who used this cement largely in building the Erie Canal. Natural cement has a powerful rival in Portland cement, due to Joseph Aspdin, of Leeds, who in 1824 mixed slaked lime and clay, highly calcined. The resulting clinker when ground, and only when ground, unites with water, the strength of the union increasing with the fineness of the grinding. Because this product looks like Portland stone, much used in England, it was given the name of Portland cement. The raw materials suitable for making it are widely distributed throughout North America, much more widely than those from which natural cement may be had. This is the principal reason why Portland cement is now produced in the United States in about six-fold the quantity of natural cement.
So rapidly has concrete grown in public favor with American builders that in 1905 they used seven-fold as much as in 1890. It has been widely adopted for pavements, as at Bellefontaine, Ohio; for breakwaters, as at Galveston and Chicago; for tunnels, as in more than four miles of the New York Subway. The foundations beneath the power-house of the Interborough Rapid Transit Company, New York, required 80,000 cubic yards; for the new station of the Pennsylvania Railroad Company, New York, a much greater quantity is being employed; in their turn these figures will be far exceeded by the needs of the new Croton Dam for the water supply of New York, and the Wachusett Dam for the water supply of Boston.