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]

[40] “Producer-gas and Gas-producers,” by Samuel S. Wyer, is a treatise of value, fully illustrated. New York, Engineering and Mining Journal, 1906. $4.00.

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:--

[41] “The Gas-engine: a treatise on the internal-combustion engine using gas, gasoline, kerosene, or other hydro-carbon as source of energy.” By F. R. Hutton, professor of mechanical engineering in Columbia University. New York, John Wiley & Sons. $5.00.

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.

To understand the Diesel principle let us begin by remembering that to the compression of a charge in a gas engine there is a moderate limit; if this be exceeded the heat of compression prematurely ignites the gases, so as to prevent due action. The air in a bicycle tire is compressed but moderately, and yet every man who has worked a bicycle air-pump with energy knows that soon its cylinder grows warm to the touch. On this very principle, that mechanical work is convertible into heat, our grandfathers had an ingenious mode of producing fire. In a syringe with a glass barrel they placed a piston fitting snugly. In a cavity of this piston they fastened a bit of cotton wool soaked in bisulphide of carbon. On forcing the piston suddenly into the cylinder, the air, quickly compressed, became hot enough to set the cotton wool on fire. The heat evolved in the compression of air is turned to account in the Diesel oil engine so as to make it the most economical converter of heat into work ever devised. First the mechanism compresses air alone to 500 pounds per square inch, then and then only the oil for combustion is injected, to take fire instantly from the heat of the compressed air. A governor regulates the period of burning; this is usually during one tenth part of the stroke, the expansion of the burned products completing the stroke. Because 500 pounds is a pressure out of the question for the compression of the mixed charge of air and combustible gas in an ordinary gas cylinder, the Diesel engine excels in economy any gas engine thus far built. At Ghent in 1903 a Diesel engine developed 165 brake horse-power from crude Texas oil with the extraordinary net efficiency of 32.3 per cent. At the St. Louis Exposition, 1904, three Diesel engines, using oil costing three cents per gallon, delivered for seven months, during eleven hours each day, at half-load, an average of 250 kilowatts at an expense for fuel of but three tenths of one cent per kilowatt hour on the switchboard, including all generator and line losses. Engineers of the first rank are convinced that the Diesel principle may be successfully embodied in gas engines. That done, with a success approaching the effectiveness of Diesel’s oil motor, we may expect steam engines and turbines to be largely dismissed from service.

Gasoline Engines.

Gasoline, although higher in price than petroleum, is commonly used in automobiles and launches. It can be atomized more quickly and fully, and without heat. To equalize motion, minimize jars, and reduce the weight of its fly-wheel, an automobile of high power has usually four cylinders with cranks set at an angle of 90 degrees with each other. The inlet valve is operated positively and, as a rule, is interchangeable with the exhaust valve. The ignition spark is furnished by a motor-driven magneto, or by a battery operating an induction coil; the lubricant is distributed by a sight-feed system, hand regulated. Cooling is effected by water circulated by a pump through jackets surrounding all cylinders and valves, each jacket having a surface of the utmost extent upon which a swiftly rotated fan drives a stream of air.

Alcohol Engines.

For some years France and Germany have used alcohol as a fuel in engines, no excise tax being imposed on alcohol employed for industrial purposes. On January 1, 1907, this will also be the case in the United States, so that we may expect alcohol to take a leading place as fuel in motors. “It has,” says Professor Elihu Thomson, “gallon for gallon less heating power than gasoline, but equal efficiency in an internal combustion engine, because it throws away less heat in waste gases and in the water jacket. A mixture of alcohol vapor with air stands a much higher compression than does a mixture of gasoline and air without premature explosion. . . . There is now beginning an application of the internal combustion engine for railroad cars on short lines which are feeders to main lines. The growth of this business may be hampered in the near future by the cost of gasoline. In this case alcohol, producible in unlimited amount, could be substituted.”

An important advantage in using alcohol is its comparative safety. In case of fire oils and gasolines float on the water intended to quench a blaze; alcohol blends with that water and the flame is subdued.

Whether oil, gasoline or alcohol be their fuel, internal combustion motors gain steadily in public acceptance. On the farm they are gradually displacing the horse. An engine, which costs nothing when it is idle, shells corn, saws wood, cuts fodder, grinds feed, separates and churns cream, drives a thrasher, turns a mill, lifts water, and performs a hundred other chores quickly, simply and cheaply.

Steam and Gas Motors United.

Mr. Henry G. Stott, chief engineer of the Interborough Rapid Transit Company, New York, has recently discussed power plant economies in so thorough and suggestive a manner as to elicit the interest of engineers the world over.[42] Basing his remarks on the records of the huge plant of his Company at 74th Street and the East River, New York, he presents this table of the average losses in converting the heat from one pound of coal into electricity:--

[42] Before the American Institute of Electrical Engineers, New York, January 26, 1906.

Heat of the coal as burned, 14,150 British thermal units 100.0% Returned by feed water heater 3.1 „ „ economizer 6.8 ------ 109.9

Loss in ashes 2.4% Loss to stack 22.7 Loss in boiler radiation and leakage 8.0 Loss in pipe radiation 0.2 Delivered to circulator 1.6 „ „ feed pump 1.4 Loss in leakage and high pressure drips 1.1 Delivered to small auxiliaries 0.4 Heating 0.2 Loss in engine friction 0.8 Electrical losses 0.3 Engine radiation losses 0.2 Rejected to condenser 60.1 To house auxiliaries 0.2 99.6 ------------ Delivered to bus-bar 10.3%

Carbon dioxide (CO²) is absorbed by a solution of caustic potash. The Ados recorder based upon this absorption has enabled Mr. Stott to learn the proportion of carbon dioxide in the gases passing to the stack, the higher that proportion, the more thorough the combustion. He finds first as an element of economy careful firing, so as to avoid “holes” or thin places in a fire, through which air wastefully pours, chilling the furnace. Next in importance is adapting draft to fuel: small anthracite requires a draft of 1.5 inches of water; with a draft of but .2 inch of water one pound of dry bituminous coal has evaporated 10.6 pounds of water, with a draft of 1 inch this fell to 8.7 pounds. Mr. Stott estimates that scientific methods of firing can reduce losses to the stack to 12.7 per cent., and possibly to 10 per cent.

Respecting the loss of 8 per cent. in boiler radiation and leakage, he maintains that this is largely due to the inefficient setting of brick which, besides permitting radiation, admits much air by infiltration. The remedy is to employ the best methods of boiler setting, such as an iron-plate air-tight case enclosing a carbonate of magnesia lining outside the brickwork.

Regarding the main loss, that of 60.1 per cent. to the condenser, Mr. Stott points out that superheating could reduce this by 6 per cent. He observes that in the higher pressures of a steam cycle a reciprocating engine has an advantage, while in the lower pressures a steam turbine is more efficient. Combine them, he remarks, and use each where it is the more profitable. But in his view for the utmost economy a new type of plant should unite both steam and gas driven units.

“Over a year ago,” he says, “while watching the effect of putting a large steam turbine having a sensitive governor in connection with reciprocating engine-driven units having sluggish governors, it occurred to me that here was the solution of the gas engine problem; for the turbine immediately proceeded to act like an ideal storage battery; that is, a storage battery whose potential will not fall at the moment of taking up load, for all the load fluctuations of the plant were taken up by the steam turbine, and the reciprocating engines went on carrying almost constant loads, whilst the turbine load fluctuated between nothing and 8,000 kilowatts in periods of less than ten seconds.

“The combination of gas engines and steam turbines in a single plant promises improved efficiency whilst removing the objection to the gas engine, namely, its inability to carry heavy overloads. A steam turbine can easily be designed to take care of 100 per cent. overload for a few seconds; and as the load fluctuation in any plant will probably not average more than 25 per cent. with a maximum of 50 per cent. for a few seconds, it would seem that if a plant were designed to operate normally with one half its capacity in gas engines and one half in steam turbines, any fluctuations of load likely to arise in practice could be taken care of.”

Discussing in detail the performance of such a plant, Mr. Stott concludes that its average total thermal efficiency would be 24.5 per cent., as against 10.3 per cent. in the plant whose record he had presented.

Heating and Power Production United.

In the bill of particulars drawn up by Mr. Stott it was shown that no less than 60.1 per cent. of the total heat from his fuel had gone into the condenser where, joined to the stream of the East River, it had been wasted. Had he used non-condensing motors the loss in exhausts would have been larger, and yet when a non-condensing motor is joined to a heating plant the whole investment may be much more profitable than where condensing motors throw away all the heat of their exhausts. Long ago some pioneer of unrecorded name, using a non-condensing steam engine, warmed his factory or mill with its exhaust steam. In summer that steam sped idly into the air, in winter it saved him so much coal that his motive power cost him almost nothing. By thus uniting the production of power and heat he showed, as few men have shown, how a great waste may be exchanged for a large profit. In the Northern States and in Canada the main use for fuel is for heating not only dwellings, but the furnaces that pour out iron and steel, the ovens that bake pottery, tiles, and so on. When but moderate temperatures are desired, as in warming a house, exhaust steam serves admirably, and so might the exhausts from gas engines. Indeed we here strike the key-note of modern fuel economy which is that wherever possible fuel should first deliver all the motive power that can be squeezed out of it, when and only when the remainder of its heat, much the larger part of the whole, should be used for warming.[43] This plan, already adopted in a good many cases, can be vastly extended with profit. In blast furnaces the first task of the fuel is performed at an extreme temperature; that work completed the gases of combustion may be purified and sent into gas engines to produce motive power at little cost.

[43] An excellent work, “The Heating and Ventilating of Buildings,” by Rolla C. Carpenter, professor of experimental engineering, Cornell University, is published by John Wiley & Sons, New York. Fourth edition, largely rewritten and fully illustrated. 1902, $4.00. It incidentally describes the best methods of heating with exhaust steam.

Heating and Ventilating by Fans.

A word was said on page 380 regarding the method now growing in favor for heating machine-shops by sending warmed air where it is needed, and not allowing it to go where it would proceed of itself and be wasted. Two illustrations show a Sturtevant ventilating fan-wheel, without its casing, and a Monogram exhauster and solid base heater, as used in many modern installations. The net gain in sending warmed air just where it does most good is comparable with the profit in mechanical draft for a furnace as compared with natural draft. Either live or exhaust steam may be used in the heating coils through which the air is forced by the fan. See also illustration on page 380.

Steam plants which furnish both heat and electricity are being rapidly multiplied throughout America. In many cases these plants supply a single large hotel, or office building. The installation at the Mutual Life Building, New York, is of 2400 horse-power, vying in dimensions with many a central plant. In Fostoria and Springfield, Ohio, in Milwaukee, Atlanta and other large cities, a central station provides heat and light and motive power to a considerable district.

District Steam Heating.

At Lockport, New York, a city of about 20,000 population, more than 350 dwellings and business premises are heated by the American District Steam Company, a concern which has installed more than 250 similar plants throughout the Union. The advantages of this system are plain:--cleanliness is promoted; customers handle no coal or ashes, tend no fires or boilers; the heat is more steadily and equably supplied than if it came from individual boilers; heat is ready day or night during the heating season; the hazard from fire is lowered and the risk of boiler explosion is abolished; water may be heated for laundries, bath-rooms and kitchens. Cheap fuel may be used, and stoked by machinery. An individual boiler in a building has to be large enough for its heaviest duty; in many cases it is called upon for but one tenth to one fifth of its full power, with much incidental waste. At a central station only as many boilers of a group are employed at a time as may be worked to their full capacity, responding to the demands of the weather.

At Lockport the steam-pipes are of wrought iron covered with sheet asbestos and enclosed in a round tin-lined wood casing, having a shell 4 inches thick, with a dead air space of about one inch between the tin and the asbestos. In its largest size this pipe has shown a total loss by radiation and conduction of but one part in four hundred in one mile; for the same distance the smallest pipe has suffered a loss of six per cent. Live steam is used at Lockport, but as a rule heating plants are supplied with exhaust steam. When intensely cold weather prevails this may be supplemented by boilers in reserve which supply live steam.

It is worth while to remark the tendency to unify, on lines of the best economy, a service of both heat and electricity. In Atlanta there were recently in operation twenty-two isolated electric plants. The central station installed a steam heating system, and as a result in less than a year all but two of the isolated plants went out of business.

Isolated Plants.

The success of the central station at Atlanta is due to the moderate scale of its charges. In the past there has been some complaint of the rates levied by central stations. In the future this complaint is likely to diminish, because an isolated plant for the production of heat and electricity was never before so low in cost, so efficient in working, as to-day. Well managed central stations broaden their market by putting a premium upon the utmost possible use of electricity. In Brooklyn, for example, the Edison Electric Company charges 10 cents per horse-power hour to customers using 100 to 250 horse-power hours per month; as consumption increases so do discounts until the customer who buys 5,000 horse-power hours pays 4 cents. The demand for current in all its diverse applications is stimulated with energy and address. A house or apartment of seven rooms is wired for twelve lights, with all fixtures complete, for $95. Signs for advertising purposes are provided _gratis_, on condition that they be lighted by the Company. The economy of a small ice machine or a refrigerator is pointed out all summer long, while in winter the comfort and convenience of electric heat is as plainly kept before the public. Such a policy as this takes account of the irrepressible facts of present day competition. When gas was the sole illuminant, producible only on a vast scale, served by an elaborate scheme of piping that from the nature of the case fell into a single hand, there was a liability to extortion. To-day in towns and cities electricity, the chief source of light, can be ground out anywhere simply, cheaply and without offence, incidentally affording when desired almost as much heat as if the fuel had been burnt to produce nothing else. Among the gifts bestowed by the electrician not the least is this conferring at the lowest price two prime necessities of life. But however liberal the management of a central station, many a fat plum will remain outside its pudding. A huge hotel, an office-building, factory, or department store, is best served by a plant of its own designed to furnish both heat and electricity, in which case the electric current will cost much less than if bought from a central station.

On occasion an isolated plant supplies a neighborhood, and at prices lower than those of a large central station which may be at a considerable distance. At Newark in the New Jersey Freie Zeitung building a 400 kilowatt plant is installed which supplies the neighbors in two blocks with electricity at 6 to 8 cents per kilowatt hour, according to the extent of their consumption. A necessary conduit crosses Campbell Street in this service. It seems likely that small power-centres of this kind, requiring no franchise, may be common in the near future, especially if united with heating systems. An inviting field for such installations is in the new residential quarters of our cities and towns, where in many cases a whole block might be cheaply and effectively served from a single plant.

Gas for Heat, Light and Power.

Heat, light and motive power may be provided either by steam or by gas. Modern industry does not tie itself to any particular servant, but chooses in turn whichever, under the circumstances of a case, will serve it well at least cost. Where natural gas is to be had at a low price it holds the field. But the area thus favored is small, so that producer gas is employed on a much larger scale. We have already seen (page 461) how coal may be gasified, valuable by-products seized, and a cheap gas be piped for miles with no liability to the condensation which befalls steam, while available for heating and for motive power. When this gas burns at a fairly high temperature, as does Dowson gas, it gives with thorium mantles a good light, so as to be an all round rival of electricity. Producer gas is preferable to solid coal because perfectly clean; it banishes the smoke nuisance, and is regulated by a touch. Mr. F. W. Harbord in his work on Steel (see page 177), says:--

“The ease with which perfect combustion of a gas can be obtained by regulating the supply of gas and air, the readiness with which it can be conducted to any required point, superheated or burned under pressure, made to give an oxidizing or a reducing flame at pleasure, and the general control that can be exercised over the size and temperature of the flame, in most cases more than compensate for the reduction in heat units due to gasification. . . . The necessity for superheating the fuel, and for keeping solid fuel out of contact with the bath of metal, make gaseous fuel indispensable in the open hearth furnace, and until Siemens solved the problem of cheap gasification of coal, this process of steel-making was impossible.”

Gaseous fuels are employed not only in steel making but in the manufacture of glass, pottery, chemicals, and much else.

When gas is used in gas engines to produce motive power, the exhausts having high temperatures may be profitably applied to heating water, or raising steam, for warming purposes.

Whether central stations employ steam or gas, or unite both, it is certain that a unification of the service of heat, light, and motive power including that required for traction, would in all our towns and cities be attended by great economy, by the abolition of much discomfort and unnecessary drudgery. A large city, such as New York or Chicago, could be supplied with these three cardinal necessities from comparatively few centres.

Electric Traction.

Such centres may, before many years elapse, be found stretching out into the distant suburbs of cities, and linking town to town. This chiefly because electricity has become a formidable rival to steam in interurban locomotion. By the time this page is printed, the New York Central & Hudson River Railroad will have begun operating its suburban trains from New York by electricity. For this service locomotives built by the General Electric Company, Schenectady, New York, will be in commission. Each will develop 2,200 to 3,000 horse-power. In careful tests a locomotive of this kind reached a speed of fifty miles an hour in 127 seconds, whereas a “Pacific” steam locomotive required 203 seconds; an important difference, especially where stops are frequent. Each locomotive, with its train of cars, weighed 513 tons. The steam locomotive with its tender weighed 171 tons; its electric rival weighed but 100 tons. So much for the gain in leaving both furnace and boiler at home, while their power is received through a special rail at rest.