Inventors at Work, with Chapters on Discovery

New York Subway.

Part of the New York Subway is of reinforced concrete. Steel rods, about 1¹⁄₄ inches square were laid at varying distances according to the different roof loads, from six to ten inches apart. Rods 1¹⁄₈ inches in diameter tie the side walls, passing through angle columns in the walls and the bulb-angle columns in the centre. Layers of concrete were laid over the roof rods to a thickness of from eighteen to thirty inches, and carried two inches below the rods, imbedding them. For the sides similar square rods and concrete were used and angle columns five feet apart. The concrete of the side walls is from fifteen to eighteen inches thick.

Bridges.

At first, properly enough, reinforced concrete was adopted with much caution in bridge-building. To-day hundreds of bridges in this material are doing service throughout the world. A good example of a small bridge is that in Forest Park, St. Louis, spanning the River des Pêres. A noteworthy design on a large scale, by Professor William H. Burr, of Columbia University, New York, has been accepted for the Memorial Bridge to cross the Potomac River at Washington. A centre-draw span of 159 feet in steel is to be flanked on each side by three spans of reinforced concrete, each of 192 feet. These spans are ribbed arches, having a rise of twenty-nine feet, with their exteriors in granite masonry. In arguing for bridges in reinforced concrete, Mr. Edwin Thacher points out that under normal circumstances their steel is not strained to much more than one quarter of its elastic limit, so that a large reserved strength is available for emergencies, while the structure is more durable than a steel bridge and ultimately more economical, comparatively free from vibration and noise, proof against tornadoes and fire, and against floods also if the foundations are protected from scour.

CHAPTER XXX
MOTIVE POWERS PRODUCED WITH NEW ECONOMY

Improvements in steam practice . . . Mechanical draft . . . Automatic stokers . . . Better boilers . . . Superheaters . . . Economical condensers . . . Steam turbines on land and sea.

In every industry a threshold question is how motive power may be had at the lowest cost. In this field within twenty years wholly new methods have been introduced, while old processes have been greatly amended. Thanks to economical water-wheels and generators, efficient transmission, and motors all but perfect, water-powers, as at Niagara Falls, now send electricity to thousands of distant workshops, to serve not only as an ideal means of actuation, but as a source of light, heat and chemical impulse. While electrical art has thus been marching forward, all the heat engines have been improved in every detail of construction. New valve-gears, economizers and superheaters, united with triple-expansion cylinders of the boldest dimensions, worked at pressures and speeds greater than ever before, combine to make the best steam engines to-day vastly more effective than those of a generation ago. And these engines are withal facing the aggressive rivalry of the steam turbines devised by De Laval, Parsons and Curtis, all much less heavy and bulky than engines, simpler to build and operate, while their motion is continuous instead of interrupted at every piston stroke.

Competing with steam motors are the new gas engines, twice as efficient in converting heat into motive power. For this reason and because much improvement seems to be feasible in their designs, and in systems for supplying them with cheap gas, their adoption on a large scale in the near future appears to be certain. Especially will this be the event should the turbine principle be as successfully applied to gas as to steam motors. Already gases from coke ovens and blast furnaces, formerly thrown away or used only in part, are being employed in gas engines with success.

To-day the production of motive power largely centres in stations so huge that they adopt with gain appliances too elaborate for use in small installations. At the power-house of the Interborough Rapid Transit Company, New York, for example, automatic machinery conveys coal from barges to vast bunkers under the roof, an even distribution being effected by self-reversing trippers. Twelve of the furnaces have automatic stokers. Ashes are removed by conveyors. Lubricating oil is pumped to high reservoirs whence it descends to flush all the bearings; it is then carried to filters from which it passes to another round of duty. It is plain that the huge scale of such a plant opens new doors to ingenuity, especially in the dovetailing of one service with another.

In some central stations, as at Findlay, Ada, and Springfield, Ohio, the exhaust steam is utilized for district heating, so that the generation of motive power is merged into the larger field of fuel economy treated as a whole. Where there is a profitable market for exhaust steam it pays to use a group of engines or turbines which are either non-condensing, or only some of which are condensing, for the aim is not simply to use the motor which asks least fuel, but to install such motors and heaters as together will earn most for the capital invested.

Steam Engines.

An experimental quadruple-expansion steam engine at Sibley College, Cornell University, has consumed but 9.27 pounds of steam of 500 pounds pressure per indicated horse-power, with a mechanical efficiency of 86.88 per cent. An Allis-Chalmers compound engine, tested December, 1905, at the Subway Power-house, New York, developed 7,300 horse-power from steam at 175 pounds pressure with a consumption of 11.96 pounds of steam per indicated horse-power. The cylinders were not steam jacketed and no reheaters were used. This engine has two horizontal high pressure cylinders, 42 inches in diameter; and two vertical low pressure cylinders, 86 inches in diameter; all of 60 inch stroke. The four cylinders work on the same crank pin, with the effect of two cranks at right angles to each other in superseded designs. A similar engine, less powerful, is shown opposite this page.

Mechanical Draft.

At this point let us put back the clock a little that we may understand why tallness in chimneys is much less in vogue for steam plants than formerly, and why this change is found to be well worth while. A device at least two centuries old is the smoke-jack, of which a specimen lingers here and there in the museums and curiosity shops of England. The rotary motion of its vanes, due to the upward draft from a kitchen fire, was employed to turn a joint of meat as it roasted in front of the coals. To-day the successors of this primitive heat-mill are the cardboard or mica toys which, fastened to a stove-pipe, or close to a lamp chimney, set at work a carpenter with his saw, a laundress with her sad-iron, and so on. These playthings show us the simplest way in which heat can yield motive power; because simplest it prevails almost universally, and yet it is wasteful in the extreme. Nobody for a moment would think of putting a wheel like that of a smoke-jack in a chimney so that the rising stream of hot gases might drive a sewing-machine or a churn, and yet for a task just as mechanical, namely, the pushing upward a chimney current itself, the heating that current to an extreme temperature is to-day the usual plan. Under good design the gases of combustion are obliged to do all the work that can be squeezed out of them; then and only then they are sent into the chimney. What if their temperature be so low, comparatively, that their rise in the stack, if left to themselves, is slow as compared with the rise in another stack of gases 300° hotter? One hundredth part, or even less, of the saved heat when applied through an engine to a fan will ensure as quick a breeze through the grate-bars as if the chimney gases were wastefully hot, and this while the chimney is but one eighth to one fourth as tall as an old-fashioned structure. This is the reason why mechanical draft is now adopted far and wide in factories, mills and power-houses. The advantages which follow are manifold: the plant is rendered independent of wind and weather, inferior fuels are thoroughly and quickly consumed, at times of uncommon demand a fire can be easily forced so as to increase the duty of the boilers. To-day in the best practice the feed water for the boilers is heated by the furnace gases just before they enter the stack; the piping for this purpose, formed into coils known as economizers, checks the chimney draft. This checking is readily overcome by mechanical draft, leaving the engineer a considerable net gain as fan and economizer are united. One incidental advantage in modern plants of sound design, and good management, is that they send forth but little smoke or none at all. With thorough combustion no smoke whatever leaves the stack.

Automatic Stoking.

The avoidance of smoke is promoted by the use of well designed mechanical stokers: two of the best are the Roney and the Jones models. The Jones apparatus forces its fuel into the fire from beneath, so that its gases, passing upward through blazing coal, are thoroughly consumed.

Boilers.

In large plants the boilers are usually of the water-tube variety, working at high pressures which may be increased at need. Mr. Walter B. Snow says:[38]—“Until the recent past the steam generator or boiler and the manner of its operation received far less attention than they deserved. Although under the best conditions over 80 per cent. of the full calorific value of the fuel may be utilized in the production of steam, this high standard is seldom reached in ordinary practice. Mr. J. C. Hoadley showed an efficiency of nearly 88 per cent. in his tests of a warm-blast steam-boiler furnace with air-heaters and mechanical draft, while Mr. W. H. Bryan has reported eighty-six tests conducted under common conditions with ordinary fuel, upon boilers of various types, which indicate an average efficiency of only 58 per cent., and have a range between a minimum of 34.6 per cent. obtained with a small vertical boiler, and a maximum of 81.32 per cent. with a water-tube boiler of improved setting. The possibilities of increased economy in ordinary boiler practice are thus clearly evident.”

Superheaters.

A cardinal improvement in steam engineering of late years has been in perfecting superheaters; this advance owes much to the mineral oils now available for lubrication at temperatures which may be as high as 675° Fahr. As steam expands to perform work it falls in temperature and much of it condenses as water, with marked loss of efficiency, with harm to its containers by severe hammering. A superheater avoids this trouble by so raising the initial temperature of the steam that condensation either ceases altogether or is much lessened. The apparatus is usually a nest of tubes placed in the fire-box close to the boiler; or, the tubes may be heated by a fire of their own, away from the boiler. The Schmidt superheater has long, parallel bent tubes, connecting two parallel headers. It may be directly applied to locomotive boilers without essential modification, and without checking the draft. On the Canadian Pacific Railway about two hundred simple locomotives have been provided with superheaters, lowering the coal consumption to 87, 85, 83 and as little as 76 per cent. in comparison with compound engines having no superheaters. At St. Louis in 1904 the Pennsylvania Railroad conducted elaborate tests of diverse locomotives. The most economical compound engine each hour used 18.6 pounds of ordinary saturated steam per indicated horse-power. Aided by a superheater this consumption was reduced to 16.6 pounds, a saving of 10.75 per cent. See page 241. In Germany portable steam engines of 150 to 220 horse-power, superheating their steam 150° to 170° Centigrade above the temperature of saturation have, in compound types, reduced their demand for steam to 12.47 pounds per horse-power hour and, in a triple-expansion model, to 9.97 pounds. In all cases the steam pipe takes the shortest possible path between its superheater and its cylinder.

Improved Condensers.

By an improved design Professor R. L. Weighton of Armstrong College, Newcastle-on-Tyne, has doubled the efficiency of the surface condenser, and reduced its consumption of water 44 per cent. In his apparatus the condensing water enters at the base, and leaves at the top, after several circuits instead of but two as in the ordinary condenser. This new apparatus is drained off in sections, instead of allowing the condensed steam to accumulate at the bottom, as in common practice. This sectional drainage is effected by dividing the interior into diaphragms somewhat inclined to the horizontal, so that the water of condensation is removed as fast as formed and does not flow from the upper tubes over those beneath. The gain in this arrangement arises from the fact that the greater part of the condensation takes place in the upper part of a condenser, where the steam impinges first upon the tubes. The Weighton apparatus, in conjunction with dry air-pumps, shows a condensation of 36 pounds of steam per square foot of surface per hour, with a reduction of pressure to one twentieth of barometric pressure (1¹⁄₂ inches as compared with 30), using as condensing water 28 times as much as the feed water, at an inlet temperature of 50° Fahr.

Steam Turbines.

For a long time, and well into the nineteenth century, water was lifted by pistons moving in cylindrical pumps. Meantime the turbine grew steadily in favor as a water-motor, arriving at last at high efficiency. This gave designers a hint to reverse the turbine and use it as a water lifter or pump: this machine, duly built, with a continuous instead of an intermittent motion, showed much better results than the old-fashioned pump. The turbine-pump is accordingly adopted for many large waterworks, deep mines and similar installations. This advance from to-and-fro to rotary action extended irresistibly to steam as a motive power. It was clear that if steam could be employed in a turbine somewhat as water is, much of the complexity and loss inherent in reciprocating engines would be brushed aside. A pioneer inventor in this field was Gustave Patrick De Laval, of Stockholm, who constructed his first steam turbine along the familiar lines of the Barker mill. Steam is so light that for its utmost utilization as a jet a velocity of about 2,000 feet a second is required, a rate which no material is strong enough to allow. De Laval by using the most tenacious metals for his turbines is able to give their swiftest parts a speed of as much as 1400 feet a second. His apparatus is cheap, simple and efficient; it is limited to about 300 horse-power. Its chief feature is its divergent nozzle, which permits the outflowing steam to expand fully with all the effect realized in a steam cylinder provided with expansion valve gear. Another device of De Laval which makes his turbine a safe and desirable prime mover is the flexible shaft which has a little, self-righting play under the extreme pace of its rotation.

The Parsons Steam Turbine.

Of direct action turbines the De Laval is the chief; of compound turbines, in which the steam is expanded in successive stages, the first and most widely adopted was invented by the Hon. Charles A. Parsons of Newcastle-on-Tyne. From an address of his to the Institute of Electrical Engineers, early in 1905, the following narrative has been taken:—

“In the early days of electric lighting the speed of dynamos was far above that of the engines which drove them, and therefore belts and other forms of gearing had to be resorted to. To make a high-speed engine, therefore, was of considerable importance, and this led to the possibilities of the steam turbine being considered. It was at once seen that the speed of any single turbine wheel driven by steam would be excessive without gearing, and in order to obtain direct driving it was necessary to adopt the compound form, in which there were a number of turbines in series, and thus, the steam being expanded by small increments, the velocity of rotation was reduced to moderate limits. Even then, for the small sizes of the dynamos at that time in use, the speed was high, and therefore a special dynamo had to be designed. Speaking generally, an increase of speed of a dynamo increases its output, and therefore it was obvious that such a high-speed dynamo would be very economical of material.

“These considerations led, in 1884, to the first compound steam turbine being constructed. It was of about 10 horse-power and ran at 300 revolutions per second, the diameter of the armature being about three inches. This machine, which worked satisfactorily for some years, is now in the South Kensington Museum. Turbines afterward constructed had two groups of 15 successive turbine wheels, or rows of blades, on one drum or shaft within a concentric case on the right and left of the steam inlet, the moving blades or vanes being in circumferential rows projecting outwardly from the shaft and nearly touching the case, and the fixed or guide blades being similarly formed and projecting inwardly from the case and nearly touching the shaft. A series of turbine wheels on one shaft were thus constituted, and each one complete in itself is like a parallel-flow water turbine, the steam, after performing its work in each turbine, passing on to the next, and preserving its longitudinal velocity without shock, gradually falling in pressure as it passes through each row of blades, and gradually expanding. Each successive row of blades was slightly larger in passage way than the preceding to allow for the increasing bulk of the elastic steam, and thus the velocity of flow was regulated so as to operate with the greatest degree of efficiency on each turbine of the series. . . . It constituted an ideal rotary engine, but it had limitations. The comparatively high speed of rotation necessary for so small an engine, made it difficult to avoid a whipping or springing of the shaft, so that considerable clearances were found obligatory, and leakage and loss of efficiency resulted. It was perceived that these defects would decrease as the engine was enlarged, with a corresponding reduction of velocity. In 1888 therefore several turbo-alternators were built for electric lighting stations, all of the parallel-flow type and non-condensing. In 1894 the machines were much improved, the blade was bettered in its form, and throughout greater mechanical strength was attained. . . . To-day (1905) under 140 pounds steam pressure, 100° Fahr. superheat, and a vacuum of 27 inches, the barometer being at 30 inches, the consumptions are in round numbers as follows:—A 100-kilowatt (134 horse-power) plant takes about 25 pounds of steam per kilowatt-hour at full load, a 200-kilowatt (268 horse-power) takes 22 pounds, a 500-kilowatt (670 horse-power) takes 19 pounds, a 1,500-kilowatt (2,010 horse-power) 18 pounds, and a 3,000-kilowatt (4,020 horse-power) 16 pounds (or 12 pounds per horse-power-hour). Without superheat the consumptions are about 10 per cent. more, and every 10° Fahr. of superheat up to about 150° lowers the consumption about 1 per cent.

“A good vacuum is of great importance in a turbine, as the expansion can be carried in the turbine right down to the vacuum of the condenser, a function which is practically impossible in the case of a reciprocating engine, on account of the excessive size of the low-pressure cylinder, ports, passages and valves which would be required. Every inch of vacuum between 23 and 28 inches lowers the consumption about 3 per cent. in a 100-kilowatt, 4 per cent. in a 500-kilowatt, and 5 per cent. in a 1,500-kilowatt turbine, the effect being more at high vacua and less at low.”

Marine Steam Turbines.

In 1894 Mr. Parsons launched his “Turbinia,” the first steamer to be driven by a turbine. Her record was so gratifying that a succession of vessels, similarly equipped, were year by year built for excursion lines, for transit across the British Channel, for the British Royal Navy, and for mercantile marine service. The thirty-fifth of these ships, the “Victorian” of the Allan Line, was the first to cross the Atlantic Ocean, arriving at Halifax, Nova Scotia, April 18, 1905. She was followed by the “Virginian” of the same line which arrived at Quebec, May 8, 1905. Not long afterward the Cunard Company sent from Liverpool to New York the “Carmania” equipped with steam turbines, and in every other respect like the “Caronia” of the same owners, which is driven by reciprocating engines of the best model. Thus far the comparison between these two ships is in favor of the “Carmania.” The new monster Cunarders, the “Lusitania” and the “Mauretania,” each of 70,000 horse-power, are to be propelled by steam turbines. The principal reasons for this preference are thus given by Professor Carl C. Thomas:—

Decreased cost of operation as regards fuel, labor, oil, and repairs.

Vibration due to machinery is avoided.

Less weight of machinery and coal to be carried, resulting in greater speed.

Greater simplicity of machinery in construction and operation, causing less liability to accident and breakdown.

Smaller and more deeply immersed propellers, decreasing the tendency of the machinery to race in rough weather.

Lower centre of gravity of the machinery as a whole, and increased headroom above the machinery.

According to recent reports, decreased first cost of machinery.[39]

CHAPTER XXXI
MOTIVE POWERS PRODUCED WITH NEW ECONOMY—Continued. HEATING SERVICES

Producer gas . . . Mond gas . . . Blast furnace gases . . . Gas engines . . . Steam and gas engines compared . . . Diesel oil engine best of all . . . Gasoline motors . . . Alcohol engines . . . Steam and gas motors united . . . Heat and power production combined . . . District steam heating . . . Isolated plants . . . Electric traction and other great services . . . Gas for a service of heat, light and power.

Gas-Power.

Steam as motive power finds its most formidable rival in cheap gases, whose familiar varieties have been long used for illumination. A simple experiment shows with what ease gas can be made, which, duly cooled, may be carried long distances without the condensation which subtracts from the value of steam. Take a narrow tube of metal or Jena glass, open at both ends: put one end near the wick of a burning candle, at the other end apply a lighted match, and at once a flame bursts forth. Here is a miniature gas-works; close to the wick inflammable gases are generated by the heat, before they have time to burn they are conveyed through the tube to a point a foot distant where, on ignition, they yield a brilliant flame. Enlarge this operation so that instead of an ounce of wax you distill tons of coal from hundreds of big retorts; set up a gas-holder as huge as the dome of the Capitol at Washington; instead of short tube lay miles of pipe through the avenues and streets of a city, and a trivial experiment widens into lighting a hundred thousand homes. So much for dividing combustion in halves, by conducting gasification in one place on a vast scale, and burning the produced gas whenever and wherever you please. One supreme advantage of the process is that coal, wood and other sources of gas much cheaper than wax or oil can be employed. Alongside the retorts which gasify coal or wood are built scrubbers which remove substances undesired in the gas,—tar, sulphur, and so on,—all salable at good prices. It was in 1792 that William Murdock, an assistant to James Watt at the Soho Works near Birmingham, there originated gas-lighting. His enterprise was a seed-plot for a variety of industries which have reached commanding importance, and are to-day expanding faster than ever before. Illuminating gas from its first introduction has on occasion wrought disaster; when it leaks through a joint into a room it rapidly unites with air; instantly on the intrusion of a flame there is a violent explosion, that is, an abrupt output of enormous energy set free under circumstances which do only harm. Can the energy, as in the case of blasting, be usefully directed?

Yes, as long ago as 1794, Robert Street designed a pump driven by the explosion of turpentine vapor below the motor piston. He was followed by inventors who used illuminating gas as their propelling agent; among these, in 1860, was Lenoir of Paris, who built a double-acting engine with a jump-spark electric igniter such as to-day is in general use. His engine consumed 95 feet of gas per hour for each horse-power, which meant that commercially the engine was a failure. Lenoir’s design has been so much improved that now large gas engines yield in motive power one fifth of the whole value of their fuel, an efficiency twice that of the best steam engines or turbines, and five-fold better than that of Lenoir’s apparatus.

Producer Gas.

How this remarkable result has been attained we shall consider a little further on, as we briefly examine the construction of a typical gas engine. At this point let us note how a gas, suitable for an engine, is manufactured at least cost, the outlay being much less than in the case of illuminating gas which represents but one third of the coal placed in the distilling retorts. Instead of this process of distillation, “producer” gas is due to a modified combustion which gasifies all the fuel. In a producer of standard type, atmospheric oxygen comes into contact with the glowing carbon of the coal or wood, forming carbon dioxide, CO². The heat generated by this union is taken up by the carbon dioxide and the nitrogen of the supplied air. These gases as they rise through the fuel bring it to incandescence so that the carbon dioxide takes up another atom of carbon, becoming carbon monoxide, CO, a highly combustible gas. Were there no impurities in the fuel, were the entering air quite free from moisture, the gases would be in volume 34.7 per cent. carbon monoxide and 65.3 per cent. nitrogen, with a heating value per cubic foot of about 118 British thermal units, a unit being the heat needed to raise a pound of water to 40° Fahr. from 39°, where its density is at the maximum. Gas thus produced is intensely hot; and as usually it contains sulphur, dust, dirt, and other admixtures, their removal by water in a scrubber would involve a waste of about 30 per cent. of the fuel heat. This loss is much diminished by sending into the producer not only air but steam, to be decomposed into oxygen and hydrogen; the oxygen combines with carbon to form more carbon monoxide, while the hydrogen is the most valuable heating ingredient in the emitted stream of gases. Were only air sent through the producer, the outflowing gases would contain nitrogen to the extent of 65 per cent.; with a charge in part air and in part steam, this percentage falls to 52; as nitrogen is useless and wastefully absorbs heat, this reduction of its quantity is gainful. By a duly regulated admission of steam, a producer is kept at a temperature high enough to decompose steam, but not so high as to send forth gases unduly hot to the purifier.

For water-gas the method is to blow steam into the fuel until decomposition ceases; the steam is then shut off, the fire allowed to recover intense heat, when more steam is injected, and so on intermittently.

A Gas Producer.

Producer gas is in more extensive use than water-gas. It is evolved in apparatus of many good designs: let us glance at the Taylor gas producer built by R. D. Wood & Company, Philadelphia. Its fuel enters in a steady stream, in controlled quantity, through a Bildt automatic feed which has a constantly rotating distributor with deflecting surfaces. The incandescent fuel is carried on a bed of ashes several feet thick, so that the coal gradually burns out and cools before its ashes are discharged. Through a conduit an airblast is carried up through this layer of ashes to where the fuel is aglow; united with this airblast is a pipe admitting steam; the united air and steam are emitted radially. In the producer walls are sight or test holes so placed that the line dividing ashes from glowing fuel may at any time be observed. When this line becomes higher on one side than the other, scrapers, duly arranged, are used. At the bottom of the producer is a Taylor rotative table which grinds out the ashes as fast as they rise above the desired depth, say every six to twenty-four hours, according to the rate of working. In large producers the ash bed is kept about three and a half feet deep, so that any coal that may pass the point of air admission has ample time to burn entirely out: in a producer with an ordinary grate such coal would fall wastefully into the ashpit. As the Taylor ash table turns it grinds the lower part of the fuel bed, closing any channels formed by the airblast, and restraining the formation of carbon dioxide, a useless product, to a minimum. A few impulses of the crank at frequent intervals maintain the fuel in solid condition, reducing the need of poking from above.

Other American producers differ from the Wood apparatus in details of design and operation; in principle all are much alike. Any good producer works well with cheap fuels, bituminous coals of inferior quality, culm, lignite, wood, peat, tanbark, and even straw from the thresher. With each of these there must be due modification of mechanism, together with means of forcing air and steam into the fire. A suction plant may be employed when superior fuels are burned, coke, anthracite, or charcoal; with currents of air and steam automatically drawn into the producer, the surrounding room is not likely to be filled with the harmful gases which may be occasionally ejected by a pressure plant.

Mond Gas.

England has gas-power installations much larger and more elaborate than those of America. Of these the most extensive have been built by the Power-gas Corporation in London, under the patents of Mond, Duff and Talbot. A Mond plant yields a gas having 84 per cent. of the calorific value of the coal consumed, which may be slack at six shillings, $1.46, per ton. Where more than thirty tons of coal per day are used, it is worth while intercepting the sulphate of ammonia, amounting to 90 pounds per ton of coal, which in small producers cannot readily be seized. Mond gas is free from tar, is cleansed of soot and dust, and holds less sulphur than ordinary producer gas. Operation is simple enough: first of all the slack is brought into hoppers above the producers. From these it is fed in charges, of from 300 to 1,000 pounds, into the producer bell, where the first heating takes place: the products of distillation pass downward into the hot zone of fuel before joining the bulk of gas leaving the producer. This converts the tar into a fixed gas, and prepares the slack for descent into the body of the producer, where it is acted upon by an airblast saturated with steam at 185° Fahr., and superheated before coming into contact with the fuel. The stream of hot gases from the producer now traverses a washer, a rectangular iron chamber with side lutes, where a water spray thrown by revolving dashers brings down the temperature of the gases to about 194° Fahr. In plants which recover the ammonia sulphate, the gas takes its way through a lead-lined tower, filled with tiles of large surface, where it meets a downward flow of acid liquor, circulated by pumps, containing ammonia sulphate with about 4 per cent. excess of free sulphuric acid. Combination of the ammonia with this free acid ensues, yielding still more ammonia sulphate. The gases, freed from their ammonia, are conducted into a cooling tower, where they meet a descending shower of cold water effecting a further cleansing before the gases enter the main pipe for delivery to consumers. In its general plan, a Mond plant resembles an illuminating gas works, especially in its seizure of profitable by-products. A ton of slack costing in England $1.46 yields 90 pounds of ammonia sulphate worth $1.92 or thereabout.[40]

Blast Furnace Gases.

For many years flames from blast furnaces and coke ovens testified to the waste of valuable gases, in especial the combustible carbon monoxide which is the main ingredient in producer gas. When we learn that coal or coke in iron-smelting parts with but three per cent. of its heat to the ore, we begin to see how grievous was the waste so long endured. For a few years past the gases sent forth from blast furnaces have been employed to heat the incoming air for the blowers, and to raise steam for engines. With twice the efficiency of steam motors the gas engine renders it well worth while to rid furnace gases of their dust and dirt so that they may not injure the mechanism they impel. An effective cleanser acts by separating the gases from their admixtures by centrifugal force. At the Lackawanna Steel Works, Buffalo, N. Y., eight gas-engines, each of 1,000 horse-power, are run on blast furnace gases. It may well prove that installations of this kind will bring other blast furnaces into cities where the sale of electricity will form a large item in the profits.

Gas Engines.

The first gas engines used gas and air at ordinary atmospheric pressure; at due intervals the charge was exploded by a glowing hot tube exposed by a slide-valve, or, according to the practice now general, by an electric spark of the jump variety. In 1862 De Rochas patented, and in 1876 Otto built, an engine on a model still in favor. Its cardinal feature is the compression of each charge. In the field of steam practice, we know how great economy is realized by beginning work with high pressures. A similar gain attends the compression of gases in a cylinder before explosion; whatever their pressure before ignition, it is trebled or quadrupled by ignition, returning a handsome profit on the work of compression, The four-cycle operation devised by De Rochas proceeds thus:—First, by drawing in a mixture of gas and air in due percentages during an outward stroke of the piston. Second, this charge is compressed by an inward piston stroke. Third, the compression charge is ignited, preferably by an electric spark, when the piston moves outward by virtue of a pressure initially extreme. Fourth, the exhaust valve opens and the spent gases are ejected as the piston returns to complete its cycle. As but one of the four piston journeys is a working stroke, it is necessary to employ a heavy flywheel to equalize the motion of the engine. When two or more engines are united, their piston rods are so connected to a common shaft as to distribute the working strokes with the best balancing effect. With four engines their piston rods may be arranged at distances apart of 90 degrees, so that one working stroke is always being exerted. This plan is adopted for the gasoline engines of automobiles so that they are served by fly-wheels comparatively small.

In his work on the gas engine, Professor F. R. Hutton discusses the advantages and disadvantages of that motor.[41] By his kind permission his main conclusions may be thus summarized, first as to advantages:—

The heat energy acts directly upon the piston, without intervening appliances. Fuel economy is greater than with steam, because there is no furnace or chimney to waste any heat. No fuel is wasted in starting the motor, or after the engine stops. The bulk, weight and cost of a furnace and boiler are eliminated, as well as their losses by radiation. A gas motor has a portability which lends itself to important industries, as logging and lumbering. It may be started at once, with no delay as in getting up a fire under a boiler; when the fuel-supply is cut off, the motor stops and needs no attention: these are important in automobile practice. Gas engines are gainfully united to systems of gas storage so that a producer may be run at high efficiency when convenient, and its gas held in holders till needed: this is helpful when a plant is worked overtime, or is liable to stresses of extreme demand at certain hours of the day. Incident to this is the advantage of subdividing power units in a large plant: each motor may receive its gas in pipes without loss, to be operated at will. The rapidity of flame propagation renders possible a high number of shaft rotations per minute, so that a multi-cylinder engine weighs little in comparison with its power. There is no liability to boiler explosion, or trouble from impurities deposited by water in a boiler. There is no exposed flame or fuel-bed requiring attention. The mechanism of the motor is simple, and its moving parts are few. A gas or oil engine furthermore enjoys a combustion which is smokeless. The fuel requires no diluting excess of air, with its cooling effect and incidental waste of energy. Dust, sparks and ashes are avoided, with diminished risk of fire. Liquid or gaseous fuel can be served by pumps or blowers so that the cost of handling is avoided.

As to disadvantages:—In a four-cycle engine there is but one working stroke in four piston traverses. In a two-cycle engine there is one working stroke in two traverses. For a given mean pressure the cylinder of a gas engine must be larger than a double acting steam cylinder. In single cylinder gas engines the crank effort is irregular; hence a heavy fly-wheel is required, or, a number of cylinders must be joined together, adding much weight. The motor does not start by the simple motion of a lever or valve. It has to be started by an auxiliary apparatus stored with energy enough to cause one working stroke. A steam engine may be overloaded to meet brief demands for extra power: not so with a gas engine. The extreme temperatures of the cylinder require cooling systems by air or water, adding weight and involving waste of energy; these temperatures furthermore may seriously distort the mechanism while rendering lubrication difficult and uncertain. Explosions of some violence may occur in exhaust pipes and passages, unless the engine is carefully adjusted and operated. Imperfect combustion clogs the working parts with soot or lampblack, especially injuring the ignition appliances. Initial pressures are so high as to cause vibration and jar. Governing is not easy, since explosion is all but instantaneous. The normal motor runs at maximum efficiency only when running at a certain speed. To vary that speed is much more troublesome and wasteful of energy than with the steam engine.

Gas engines united to gas producers have been employed with success on shipboard. This field, with its high premium on fuel reduction, which means more space for cargo, is likely to be largely developed in the near future. Soon, also, we may expect locomotives to exhibit a like combination with profitable results.

Steam and Gas Engines Compared.

During 1904 and 1905 the U. S. Geological Survey compared at St. Louis a steam engine with a gas engine, each of 250 horse-power, using 24 varieties of lignites and bituminous coals. The steam engine was of a simple, non-condensing, unjacketed Corliss type, from the Allis-Chalmers Company, Milwaukee. The gas engine was a three-cylinder, vertical model from the Westinghouse Machine Company, Pittsburg. Its gas was supplied by a Taylor gas producer furnished by R. D. Wood & Company, Philadelphia, of the design illustrated on page 460.

The official report in three parts, fully illustrated, presenting the tests in detail, was published by the Survey early in 1906. On page 978, of the second part, 14 comparative tests are summarized. They show that in the gas plant on an average 1.70 pounds of fuel were consumed in producing for one hour one electrical horse-power; in the steam plant the consumption was 4.29 pounds, two and a half times as much. With apparatus adapted to a particular fuel, with larger and more economical engines, better results would have been shown both by steam and gas. Yet competent critics believe that the ratio of net results would have remained much the same. The most important fact brought out in the tests is that some fuels, lignites from North Dakota for example, have little worth in raising steam, and high value in producing gas; their moisture is a detriment under a boiler, it is an advantage in a gas producer. The cost of this investigation is likely to be repaid many thousand-fold in pointing out the best way to use fuels which abound in the Western and Northwestern States and in Canada. See note, page 241.

Oil Engines.

In some cases petroleum is the best available fuel for an engine, essentially much the same as a gas motor. A carburetor, or atomizer, blows the oil into a fine mist almost as inflammable as gas. In small sizes for launches, threshing machines, or work-shops of limited area, the petroleum engine is a capital servant. In sizes of 75 horse-power and upward the Diesel engine is not only the best oil engine but the most efficient heat-motor ever invented. It involves a principle as important as that of Watt’s separate condenser for the steam from his cylinder.