Inventors at Work, with Chapters on Discovery

Of late years cutters driven by compressed air have been largely adopted throughout the coal mines of the United States. A cutter weighing ten pounds, with air at seventy-five pounds behind it, strikes a blow 160 to 250 times a minute, beginning at the floor and making as little slack as a hand pick intelligently wielded. Other tools, in great diversity, actuated in the same way, ask only skill in guidance instead of muscular drudgery. Air drills are used in mines, wells, tunnels, and rock foundations; at will the mechanism impels a hammer instead of a drill. Air riveters build ships and bridges, as well as fasten together the comparatively small plates of boilers and fire-boxes. With a little variation in its form we have a tool which caulks boilers, tanks, and ships. Air-hammers light and strong have revolutionized the art of cutting and carving stone, the force of a stroke being regulated by a touch. Pneumatic hammers are of two kinds: Valveless hammers in which the piston is the hammer, opening and shutting the inlet and exhaust parts; and valve hammers, in which there is a distinct moving valve. Hammers without valves are always short of stroke, and are chiefly used in caulking and chipping. Some of them yield as many as 250 strokes per minute. Valve hammers do not move at this high pace, rarely exceeding thirty-five strokes per minute, but each stroke is comparatively long and forcible for riveting and the like severe work. In the Keller hammer the valve moves longitudinally with the hammer barrel and in the same direction with the hammer piston, instead of in the opposite direction as is usually the case. A blow, therefore, tends to seat the valve all the more firmly, instead of jarring it off its seat. Another result is that the tool works efficiently even when the valve is loosened by much use. This hammer is manufactured by the Philadelphia Pneumatic Tool Co., Philadelphia.

It is interesting to learn from Mr. W. L. Saunders, of New York, how the air-tools just considered were introduced. He says:—

“Mr. McCoy is entitled to the credit of first applying pneumatic tools to heavy work, such as chipping metals, caulking boilers, cutting stone and so on. He was not, however, the originator of the broad idea, as long before he perfected the tool for heavy work it had been used as a dental plugger, a device working compressed air in a cylinder so that a piston struck the end of a tamping tool, used to insert gold into the cavities of teeth.”

A rock drill, on occasion, may serve as a blacksmith’s hammer. The drill, detached from its tripod, is fastened to a vertical support. The ram, duly supplied with compressed air, is fixed in position over the anvil, upon which it descends more frequently if less forcibly than a steam hammer. A rock drill may also serve to drive drift bolts into the timbers of caissons. This task when effected by ordinary sledge hammers is slow and costly, while with compressed air as a servant capital work is done at much lower expense. The drill is provided with handles so as to be readily managed by two men, who place the anvil, with its cupped end, on the head of the bolt to be driven. Pneumatic energy does the rest.

With dimensions much enlarged an air-driven piston becomes a rammer for foundry sand, for roads and pavements, for tamping the beds of railroads. In foundries a moulder is furnished with a small sand-sifter, vibrated by compressed air; he is now free to use his shovel all the time, so that he does five times as much work as before. Hoists small and large are actuated by the same agency; in every case the mechanism is so simple that rough usage is withstood and repairs, when needed, are easily effected. If a ratchet, a pawl, a bearing, wears out, a new one can be bought at small cost and at once fitted into place. Designers have produced rotary as well as reciprocating air tools; of these a wood-borer is a capital example.

Sometimes it is well worth while to employ compressed air simply as a blast to keep a milling-cutter free from its chips; when the blast is cold, as it usually is, the cutter may turn all the quicker.

Compressed air can do much else than impel pistons of familiar type. In one remarkable device it has put pistons out of business altogether.

Air-Lifts.

Fill a tumbler to the brim with water, take a straw and dip it to the bottom of the glass, blowing as heartily as you can. At once the water overflows because displaced by rising bubbles of air. Instead of a tumbler take a long upright pipe filled with water, send to its base compressed air of adequate pressure, and you have the Pohle air-lift, which carries water into the reservoirs of Fort Madison, Iowa, of Dixon, Illinois, of Asbury Park, New Jersey, and many other towns and villages. On a smaller scale the air-lift brings up water from thousands of wells, rivers, and lakes. Aboard ship it moves water ballast from one compartment to another, so as to give the vessel just the trim or inclination desired. In chemical works it raises liquids so corrosive that no other lifter is feasible. It has no valves or other moving parts to be deranged or hurt in case its stream bears sand or dirt, so that it is a capital drainage pump; after serving thus it may bring sewage to farms and distribute it thoroughly. To be fairly efficient the air-lift requires that two thirds of the length of its upright pipe be immersed below the surface of the liquid to be raised.

Liquids Lifted by Expanding Air.

For oil wells, which may be 2000 or more feet in depth, a lifter not so simple is employed. A pipe, comparatively large, is lowered to the oil. Its base forms a receiver which, at will, may be closed on its earthward side, then through a small inner tube compressed air reaches the oil to force it bodily to the surface of the ground. The Harris pump lifts oil, water, or other liquids with high efficiency: it allows the compressed air after use to act expansively; this helps to drive the compressor; then this expanded air is once more highly compressed, and so recurrently.

A Jack-of-All-Trades.

Compressed air readily moves liquids as masses; it as easily impels them as particles. A lady’s toilet table usually displays an atomizer. Its rubber bulb, sharply squeezed, emits a tiny stream of perfume as a quick air blast breaks a drop of liquid into spray. Magnify this apparatus and you have a painting machine for freight and passenger cars, fences, and out-buildings. Driven as it is with projectile force the pigment penetrates further than if laid on by hand, reaching crannies and crevices which evade a brush. On the same principle Hook’s spraying machine sends Bordeaux mixture into the foliage of an orchard, or delivers a solution of carbolic acid upon the floors, walls, and ceilings of a hospital or a sick-room. Strengthen such a blast and you can elevate, dry, and aerate grain, or lift the culm from a coal heap to a furnace, and then discharge the ashes as they tumble from a grate. Where stretches of water are sandy and muddy, compressed air dredges a channel by stirring up deposits at the bottom.

Removing Dust and Dirt.

An air compressor reversed in direction is an air exhauster, such as we find carrying money in department stores. The powerful in-draft of this apparatus, often drawing large pieces of paper or card into the pipes, has led to the invention of a means of removing dust and dirt, admirable in thoroughness. A receiver, shaped to suit its special task, is passed over pictures and their frames, upholstery, carpets or bare floors, and through the flexible pipe attached to its handle, dust and dirt are borne into a reservoir where they are caught by water for due removal. Ordinary sweeping with a broom, the usual wielding of a feather duster, or a blast of compressed air, but stir up dust and dirt for harmful redistribution. This “vacuum” cleaning method takes dust and dirt wholly away, and with wonderful celerity. See picture opposite page 164. It is astonishing to see a pound of fine flour removed from a thick carpet in twelve seconds, leaving behind not one visible particle. This plan cleanses carpets without their being lifted from floors, or a billiard cloth just as it stands on a table. This service greatly promotes health; the further the physician goes with his microscope the more convinced is he that dust is one of the chief carriers of disease.

Not only dust but sand may be borne when a breeze rises to a gale.

Sand-blast.

In Lyell’s Bay, near Wellington, New Zealand, and in many other places throughout the world, flints have been found so beautifully and symmetrically polished that they were at first believed to be products of art, yet nothing but wind-blown sand had given them form. Fifty years ago globes for gas jets were frosted by a handful of sand quickly thrown from side to side for a few minutes. Strange to say, gunnery was to supply the link to carry sand to labors of much greater moment.

General B. C. Tilghman, of Philadelphia, one day noticed the much worn touch-hole of an old bronze cannon. He felt sure that the wear had been due not so much to outflowing gases as to bits of unburnt powder driven out at each discharge, identifying this abrasion with the roughening of glass in windows facing sandy shores of the sea. In 1870 he began experiments by blowing sand jets with a fan, soon discovering that he had hit upon a cheap and easy means of frosting glass, carving stone, and scouring castings. He was astonished to find that sand readily pierced materials harder than itself, as corundum and toughened steel. To-day the sand-blast executes many new tasks: it resurfaces stone buildings which have become discolored and grimy; it cleanses metallic surfaces for the welder, the electroplater, the enameler; it renews files and rasps; it removes scale from boilers, paint and rust from steel bridges and other structures. The apparatus manufactured by Mr. C. Drucklieb, of New York, designed much in the form of a steam injector, employs air at a pressure of about twenty pounds to the square inch.

Air Compressors.

Compressed air is at work on so large a scale that its economical production and use are matters of consequence. Mechanism for both purposes, of the best design, involves a few simple principles. Suppose we have a cylinder, fourteen inches long, and that with a piston we force the contained air within one inch of its base, so as to occupy ¹⁄₁₄ of its original volume. This act of compression, which we will imagine to be all but instantaneous, will heat the air through 613° Fahr., so that if at 60° when the operation begins, the air will be 673° at the end. Suppose, further, that this air parts with no heat to surrounding metal, and that the piston moves without friction; the compressed air on being allowed to expand will return all the work expended in compression, and resume its first temperature, 60°. If air would serve us in this ideal way, we would have an agent with all the good points of steam and none of its drawbacks. In actual practice several items left out of our imaginary picture must be reckoned with. Air heated in compression quickly warms surrounding masses and has to be cooled when sent off on distant errands, losing much working power in the process. The very act of compression retards itself: the air, because heated, has additional elasticity for the compressor to overcome.

Plainly, the engineer should begin by sending into his compressor air as cool as possible, and during compression he should keep the temperature of the air as low as he can. Moderate pressures, to fifty pounds per square inch or so, may well be effected at a single stroke, the air as it issues from the compressing cylinder passing through pipes immersed in cold water, a similar chilling stream being sent around the cylinder walls themselves. This air at fifty pounds, duly cooled, may now, if we wish, be brought to say 100 pounds pressure in a second cylinder; its output is in turn cooled as before by conveyance through pipes bathed in cold water. The more thorough the cooling, the less moisture will the air contain to give trouble afterward by condensing in pipes or machinery. If a pressure higher than 100 pounds to the square inch is in request, a third compressor may be linked to the second. In some installations, where extreme pressures are attained, four-fold apparatus is employed; its chief economy rests in cooling the air at four distinct stages, greatly diminishing the work which otherwise would have to be wastefully done.

With the energy of steam economically converted into the energy of compressed air, the engineer sends his new servant as far as he pleases. Let us imagine that a mile off he wishes to drive a gang of saws. He will soon notice that the exhaust pipe is very cold, and if the compressed air was not well dried as produced, its moisture will now be deposited not as water merely, but as frost to check the machinery. This is because air, like steam, falls in temperature as it expands at work; that fall measuring the heat-equivalent of the work performed. For the chill which the engineer observes, he has a simple remedy; he surrounds the air pipe, as it enters its machinery, with a small heater, fed with coke, coal, or oil. At once all frost vanishes, and the air with added elasticity is vastly more effective than before. By no other means can so much work be won from fuel as through this device. In some cases a heater has yielded 1.25 horse power for an hour in return for each pound of coal it has burned.

In producing compressed air, inventors step by step have kept in view the best steam practice. It was long ago observed that working steam when wholly expanded in one cylinder chills itself, imparting its chill to the cylinder walls so that they seriously cool the next charge of steam, lowering its value for motive power. In a multiple expansion engine of four successive cylinders, each in turn receives the steam, which with thorough jacketing is maintained at the highest temperature possible. Keeping to converse lines the compressor divides its task into stages, at each of which a desired change of temperature can be easily effected. With steam this change consists in adding heat; with compressed air it consists in abstracting heat.

A Centralized Air Plant.

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.

Concrete has long been adopted for a variety of less ambitious purposes. At St. Denis, near Paris, it was many years ago molded into a bridge of modest span. It has formed thousands of dwellings in factory and mining villages and towns, as well as many villas of handsome design. It is particularly well adapted for silos, as here illustrated.[36] All this expansion of an old art has been stimulated by a steady reduction in the price of Portland cement, and by constant improvement in its quality. As the manufacture has expanded, its standards have risen, its machinery has become more economical and trustworthy in results. While the cost of concrete has thus been lowered by a fall in the price of cement, the wages of bricklayers and stone-masons have advanced, adding a new reason for building in concrete, since it requires in execution but little skilled labor. The good points of concrete are manifold; it forms a strong, fire-resisting, and damp-proof structure. For mills and factories another item of gain is that it forms a unit such as might be hewn out of a single huge rock, vibrating machinery therefore affects it much less than it does an ordinary building. At the same time its walls and floors obstruct sound, conducing to quiet. Concrete must be honestly made and used, otherwise, just as in the case of rubbishy bricks, ill laid, it may tumble down from its own weight. And furthermore it is necessary to recognize how widely concretes of diverse composition vary in strength and durability. There should be a careful adaptation in each case of quality to requirement. Concrete walls, as first produced, had a forbidding ugliness; this is being remedied by surfacings of pleasant neutral tones. A well designed residence executed in concrete at Fort Thomas, Kentucky, is shown opposite this page.

In Mr. Edison’s judgment a vast field awaits the concrete industry in building small, cheap dwellings. He once said to me, as he spoke of his cement mill,—“What I want to see is an architect of the stamp of Mr. Stanford White of New York take up this material. Let him design half a dozen good dwellings for working people, all different. Each set of molds, executed in metal, would cost perhaps $20,000. Such dwellings could be poured in three hours, and be dry enough for occupancy in ten days. A decent house of six rooms, as far as the shell would go, might cost only three hundred dollars or so. It would be stereotypy over again and the expense for the models would disappear in the duplications repeated all over the country.”

Concrete is now supplied to builders in blocks, usually hollow and much larger than bricks. When cast in sand they look like stone. Of course, subjected as they are to more than ordinary stresses, their production demands special care. The methods, therefore, which are adopted in manufacturing these blocks may be taken as the best practice in the industry broadly considered. Says Mr. H. H. Rice, of Denver:—“The sand employed should be sharp, silicious and clean. The gravel used should contain a fair proportion of as large sizes as can be advantageously employed in the particular machine used. Where gravel is not available, crushed stone takes its place. Care should be exercised to obtain stone as strong as the mortar. What proportions of sand, gravel and broken stone should be mixed together is a question determined by the extent of their voids: these may vary from one third to one half the whole volume. Assuming that we have to deal with the larger fraction, a mixture of 1 cement, 2 sand, 4 gravel, should be employed; this is classified as the lowest grade of fat mixture. At times a lean mixture, 1 cement, 3 sand, 5 gravel, might be advantageously adopted. Where gravel or broken stone is not used, the proportion of cement to sand should be as 1 to 4. A fat mixture has greater tensile strength than a lean mixture, but resistance to compression depends upon a thorough filling of voids. A lean mixture thoroughly worked, proves more satisfactory than a fat mixture with hasty and indifferent handling. With any mixture success is attained only by completely coating every grain of sand with cement, and every piece of stone or gravel with the sand-cement mortar. (See Mr. Umstead’s results, page 240.)

In producing concrete blocks there are three different methods, tamping, pressing, and pouring, each adapted to a particular mixture for a special kind of work. Two-piece walls, devised in 1902, deserve a word of description. The pressed blocks of which they are built show the new freedom conferred by concrete as a building material. Each block has a long right-angle arm extending inward from the middle, and a short arm extending from each end. In laying the blocks in a wall no portion of a block extends through the wall. By leaving the exterior vertical joints open to afford a free circulation of air, no part of a block on one side of the wall touches any block from the opposite side; this prevents the passage of moisture and produces in effect two walls, tied by the overlapping arms or webs in alternate courses, and affording in its bond a great resistance to lateral stresses. Blocks in other forms equally useful are steadily gaining popularity.[37]

Concrete, although widely available to the builder, is in many cases a material he cannot employ. For a store-house, thickness of wall, ensuring an equable temperature, is an advantage; for an office-building, reared on costly ground, this thickness is out of the question. Beams, too, cannot have much length in a material which is only one tenth as strong in tensile as in compressive resistance. Clearly the scope for concrete by itself was to be limited unless it could find a partner able to confer strength while adding but slight bulk. An experiment of the simplest was to be the turning point in a great industry.

Concrete Reinforced by a Backbone of Steel. Joseph Monier, the Pioneer.

Concrete, as one of its minor uses, had often been molded into tubs for young trees and shrubs. In 1867, Joseph Monier, a French gardener, in using tubs of this kind found them heavy and clumsy. By way of improvement he built others in which he embedded iron rods vertically in the concrete, securing thus a strong frame-work which permitted him to use but little concrete, and make tubs comparatively light and thin. Monier was not a man to rest satisfied with a single step in a path of so much promise. Before his day builders had joined concrete and metal, but without recognizing the immense value of the alliance. He proceeded to build tanks, ponds, and floors of his united materials, at length rearing bridges of modest proportions. His work attracted attention in Germany and Austria, as well as at home in France, so that soon reinforced concrete, as it was called, became a serious rival to brick and stone. For two thousand years and more, concrete had been a familiar resource of the builder; to-day with a backbone of steel it fills an important place between masonry and skeleton steel construction, boldly invading the territory of both.

Disposal of Steel in Reinforced Concrete.

Reinforced concrete has been thoroughly studied with regard to its properties and the forms in which it may be best disposed. Since the strength of concrete is usually ten-fold greater in compression than in tension, designs should be compressive whenever possible, all tensile strains being carefully committed to the steel. In arched bridges the strains are chiefly compressive, hence the success with which they are executed in reinforced concrete. Mr. Edwin Thacher of New York, eminent in this branch of engineering, sees no reason why spans of 500 feet should not be feasible and safe. Some remarkable discoveries have followed upon experiments with reinforcement diverse in form and variously placed within a mass. To increase the strength of a square steel bar Mr. E. L. Ransome twists it into spiral form; on square steel bars Mr. A. L. Johnson places projections; Mr. Edwin Thacher rolls his steel into sections alternately flat and round. All these contours have large surfaces at which metal and concrete adhere. Reinforcing bars designed by Mr. Julius Kahn and by the Hennibique Construction Company are smooth, and slightly bent from straightness at intervals. In every case the question is, Where will the tensile strength of the steel do most good, because most needed? M. Considere has found that concrete hooped with steel wire has more than twice the resistance of concrete in which an equal amount of steel is centrally placed. In his floor constructions M. Matrai gives steel wires the curves they would take under a load. Keeping to its original lines the Monier reinforcement of to-day consists in a rectangular netting of rods or wires. Somewhat similar is the expanded metal backing invented by Mr. J. F. Golding; it is sheet steel pierced with parallel rows of slits which are expanded until the metal assumes the form shown in an accompanying illustration. A lock woven-wire fabric of galvanized steel wire is made by W. N. Wight & Company, New York, in any desired size of mesh, with an ultimate strength of 116,000 pounds per square inch of metal.

For piling, reinforced concrete is extensively used. Its independence of moisture, its exemption from the ravages of the teredo, render it much preferable to timber for marine work.

Molds for Reinforced Concrete.

Reinforced concrete, like every other new building material, has called forth ingenuity in many ways. When, for instance, a factory is to be reared much inventive carpentry is required to plan and construct the forms, or molds, into which the liquid concrete is to be poured around the steel skeletons. The footings, outside and inside columns, walls, girders, beams, floor-plates, roofs, and stairs all require separate forms, intelligently devised with a view to economy. For the Ingalls Building, Cincinnati, the forms cost $5.85 per cubic yard of concrete in place. White pine is the best wood for the purpose; it is readily worked and keeps its shape when exposed to wind and weather. For common buildings a cheaper wood, spruce or fir, may be chosen; even hemlock will serve if a rough finish suffices. In most cases green lumber is preferable to dry as less affected by water in the concrete. In fine work the boards of which the molds are made are oiled, and may be used over and over again. In all tasks a strict rule is that the reinforcing metal be properly placed and remain undisturbed as work proceeds.

Buildings of Reinforced Concrete.

The Pugh Power Building, erected for manufacturing purposes in Cincinnati, is a capital example of what can be done with reinforced concrete. It is 68 feet wide, 335 long, and 159 high; its columns are spaced fourteen to seventeen feet longitudinally, twenty to twenty-three feet transversely; the floors are figured to bear a load of 230 pounds per square foot. In the same city is the Ingalls Building, for offices, 100 by 50 feet, and 210 feet high, designed by Mr. E. L. Ransome of New York. Among other structures of his design, executed in the same material, is the St. James Episcopal Church, Brooklyn, New York; buildings for the United Shoe Machinery Company, Beverly, Massachusetts, and piano factories for the Foster-Armstrong Company, Despatch, New York. The inspection shops of the Interborough Rapid Transit Company, West 59th Street, New York, are also of reinforced concrete: no wood is used in wall or roof.

Reinforced concrete forms nine bins in one of the grain elevators of the Canadian Pacific Railway at Port Arthur, Ontario, on the shore of Lake Superior. The walls are nine inches thick, reinforced horizontally and vertically to a height of ninety feet and a diameter of thirty feet. There are also four intermediate bins, the whole thirteen holding 443,000 bushels. At South Chicago the Illinois Steel Company has built four similar bins for the storage of cement, each twenty-five feet in diameter and fifty feet high, with walls five to seven inches thick.

Many chimneys have been built of the new material; notably the chimney for the Pacific Coast Borax Company, Bayonne, New Jersey, 150 feet high, with an interior diameter of seven feet. These dimensions are exceeded at Los Angeles, California, where a chimney for the Pacific Electric Company rises 174 feet above its foundations, with an inside diameter of eleven feet. Both structures have hollow walls of the Ransome type reinforced horizontally and vertically.

That reinforced concrete serves to build chimneys and flues is proof of its fire-resisting quality. Concrete is a slow conductor of heat, and both it and steel have almost the same slight expansibility as temperatures rise, so that they remain together in a fire. Terra cotta, which expands much more than steel when heated, cracks off from the metal it was intended to protect, leaving it to bend or fuse in a blaze. Concrete, furthermore, behaves well when its temperature is suddenly lowered, as when a fireman dashes a stream of water upon it at a fire. No wonder, then, that the reinforced concrete is more and more in request in cities as the material for buildings rising higher and standing more thickly on the ground than did buildings of old. In the great fire in San Francisco, April, 1906, reinforced concrete withstood extreme temperatures much better than any other material. It will be largely used in rebuilding the city.

Resistance to Fire and Rust.

Frequently the question is asked, Is the steel in reinforced concrete liable to corrosion, so that its walls are likely to become weak and insecure after a few years? With careful planning and faithful workmanship the results prove to be worthy of confidence. Professor Charles L. Norton of Boston has taken steel, clean and in all stages of corrosion, and embedded it in stone and cinder concrete, wet and dry mixtures, in carbon dioxide and sulphurous gases; other specimens were intermittently exposed to steam, hot water, and moist air for one to three months. Duly protected by an inch or more of sound concrete the steel was absolutely unchanged while naked steel vanished into streaks of rust. Mr. Ransome says that in tearing up a stretch of sidewalk in Bowling Green Park, New York, in use twenty years, some embedded steel rods were found in perfect condition. The Turner Construction Company, of New York, exposed concrete blocks in which steel bars were embedded, and laid them on a beach at low tide where they were covered by salt water three or four hours every day; after nine months’ exposure the blocks were broken disclosing the bars free from rust. Professor Spencer B. Newberry records that a water main at Grenoble, France, built on the Monier system, twelve inches in diameter, eighteen inches thick, containing a framework of ¹⁄₁₆ and ¹⁄₄ inch steel rods, was found perfectly free from rust after fifteen years’ service in damp ground. He also states that a retaining wall of reinforced concrete in Berlin was examined after eleven years’ use and the metal found uncorroded, except in some cases where the rods were only 0.3 or 0.4 inch from the surface.

Tanks, Standpipes, Reservoirs.

This waterproof quality of reinforced concrete recommends it as a material for tanks and reservoirs. In 1903 a water tower was built at Fort Revere, Massachusetts, for the United States Government, ninety-three feet in height, octagonal in section, enclosing a tank twenty feet wide, fifty feet high, with walls six inches thick at the bottom, three at the top, coated inside with an inch of Portland cement. At Louisville, Kentucky, a reservoir has been built 394 by 460 feet, and about twenty-five feet high. Its walls and columns are concrete, its roof is in reinforced concrete disposed as groined arches, each of nineteen feet clear span. A reservoir wholly of reinforced concrete at East Orange, New Jersey, is 139 by 240 feet, with a height of 22¹⁄₃ feet. In the early days reinforced concrete was used for water-pipes: more than a hundred miles of such pipes are now in service in Paris. Water-pipes on the Coignet system employ thin steel rods hooked at both ends and curved into encircling hoops. Other rods laid lengthwise run through the hooks, so as to hold each part of the framework securely in place. At Newark, New Jersey, 4,000 feet of single and 1,500 feet of double 60-inch conduits, reinforced with 3-inch expanded steel, have been recently laid.

The material thus available for systems of water supply is also impressed into tasks of sewerage. In Harrisburg, Pennsylvania, a sewer of this kind three miles long intercepts all other sewers, carrying the whole stream below the city to an outfall in the Susquehanna River. A water culvert, for somewhat similar duty, may on occasion be so heavily reinforced as to carry railroad tracks with safety, as in a culvert for a Western railroad shown in an accompanying figure.