Gay-Lussac, continuing his investigations as to expansion of air and gases under increased temperatures, in 1807-10, established the law that when free from moisture they all dilate uniformly and to equal amounts for all equal increments of temperature. He also showed that the gases combine, as to volume, in simple proportions, and that several of them on being compounded contracted always in such simple proportions as one-half, one-third, or one-quarter, of their joint bulk. By these laws all forms of engines which were made to work through the agency of heat are cla.s.sed as heat engines--so that under this head are included steam engines, air engines, gas engines, vapour engines and solar engines. The tie that binds these engines into one great family is temperature. It is the heat that does the work. Whether it is a cannon, the power of which is manifested in a flash, or the slower moving steam engine, whose throbbing heart beats not until water is turned to steam, or the sun, the parent of them all, whose rays are grasped and used direct, the question in all cases is, what is the amount of heat produced and how can it be controlled?

It, then, can make no difference what the agent is that is employed, whether air, or gas, or steam, or the sun, or gunpowder explosion, but what is the temperature to be attained in the cylinder or vessel in which they work. Power is the measure of work done in a given time.

Horse power is the unit of such measurement, and it consists of the amount of power that is required to raise one pound through a vertical distance of one foot. This power is pressure and the pressure is heat.

The unit of heat is the amount of heat required to raise the temperature of a pound of distilled water one degree--from 39 degrees to 40 degrees F. Its amount or measurement is determined in any instance by a dynamometer.

These were the discoveries with which Philosophy opened the nineteenth century so brilliantly in the field of Pneumatics.

Before that time it seemed impossible that explosive gases would ever be harnessed as steam had been and made to do continual successful work in a cylinder and behind a piston. As yet means were to be found to make the engine efficient as a double-acting one--to start the untamed steed at the proper moment and to stop him at the moment he had done his work.

As Newcomen had been the first in the previous century to apply the steam engine to practical work--pumping water from mines--so Samuel Brown of England was the first in this century to invent and use a gas engine upon the water.

Brown took out patents in 1823 and 1826. He proposed to use gunpowder gas as the motive power. His engine was also described in the _Mechanics' Magazine_ published in London at that time. In the making of his engine he followed the idea of a steam engine, but used the flame of an ignited gas jet to create a vacuum within the cylinder instead of steam. He fitted up an experimental boat with such an engine, and means upon the boat to generate the gas. The boat was then operated upon the Thames. He also succeeded experimentally in adapting his engine to a road carriage. But Brown's machines were c.u.mbrous, complicated, and difficult to work, and therefore did not come into public use.

About this time (1823), Davy and Faraday reawakened interest in gas engines by their discovery that a number of gases could be reduced to a liquid state, some by great pressure, and others by cold, and that upon the release of the pressure the gases would return to their original volume. In the condensation heat was developed, and in re-expansion it was rendered latent.

Then Wright in 1833 obtained a patent in which he expounded and ill.u.s.trated the principles of expansion and compression of gas and air, performed in separate cylinders, the production of a vacuum by the explosion and the use of a water jacket around the cylinder for cooling it.

For William Burdett, in 1838, is claimed the honour of having been the first to invent the means of compressing the gas and air previous to the explosion, substantially the same as adopted in gas engines of the present day.

The defects found in gas engines thus far were want of proper preliminary compression, then in complete expansion, and finally loss of heat through the walls.

Some years later, Lenoir, a Frenchman, invented a gas engine of a successful type, of which three hundred in 1862 were in use in France.

It showed what could be accomplished by an engine in which the fuel was introduced and fired directly in the piston cylinder. Its essential features were a cylinder into which a mixture of gas and air was admitted at atmospheric pressure, which was maintained until the piston made half its stroke, when the gas was exploded by an electric spark. A wheel of great weight was hung upon a shaft which was connected to the piston, and which weight absorbed the force suddenly developed by the explosion, and so moderated the speed. Another object of the use of the heavy wheel was to carry the machine over the one-half of the period in which the driving power was absent.

Hugon, another eminent French engineer, invented and constructed a gas engine on the same principle as Lenair's.

About this time (1850-60) M. Beau de Rohes, a French engineer, thoroughly investigated the reasons of the uneconomical working of gas motors, and found that it was due to want of sufficient compression of the gas and air previous to explosion, incomplete expansion and loss of heat through the walls of the cylinder, and he was the first to formulate a "cycle" of operations necessary to be followed in order to render a gas engine efficient. They related to the size and dimensions of the cylinder; the maximum speed of the piston; the greatest possible expansion, and the highest pressure obtainable at the beginning of the act of expansion. The study and application of these conditions created great advancements in gas engines.

With the discovery and development of the oil wells in the United States about 1860 a new fuel was found in the crude petroleum, as well as a source of light. The application of petroleum to engines, either to produce furnace heat, or as introduced directly into the piston cylinder mixed with inflammable gas to produce flame heat and expansion, has given a wonderful impetus to the utilisation of gas engines.

G. H. Brayton of the United States in 1873 invented a very efficient engine in which the vapour of petroleum mixed with air const.i.tuted the fuel. Adolf Spiel of Berlin has also recently invented a petroleum engine.

Princ.i.p.al among those to whom the world is indebted for the revolution in the construction of gas engines and its establishment as a successful rival to the steam engine is Nicolaus A. Otto of Deutz on the Rhine.

In the Lenair and Hugon system the expansive force of the exploded gas was used directly upon the piston, and through this upon the other moving parts. A great noise was produced by these constant explosions.

In the Otto system the explosion is used indirectly and only to produce a vacuum below the piston, when atmospheric pressure is used to give the return stroke of the piston and produce the effective work. The Otto engine is noiseless. This is accomplished by his method of mixing and admitting the gases. He employs two different mixtures, one a "feebly explosive mixture," and the other "a strongly explosive mixture," used to operate on the piston and thus prolong the explosions.

The mode of operation of one of Otto's most successful engines is as follows: The large fly wheel is started by hand or other means, and as the piston moves forward it draws into the cylinder a light charge of mixed coal gas and air, and the gas inlet is then cut off. As the piston returns it compresses this mixture. At the moment the down stroke is completed the compressed mixture is ignited, and, expanding, drives the piston before it. In the second return stroke the burnt gases are expelled from the cylinder and the whole made ready to start afresh.

Work is actually done in the piston only during one-quarter of the time it is in motion. The fly-wheel carries forward the work at the outset and the gearing the rest of the time.

Otto was a.s.sociated with Langen in producing his first machine, and its introduction at the Centennial Exposition at Philadelphia in 1876 excited great attention. Otto and E. W. and W. J. Crossley jointly, and then Otto singly, subsequently patented notable improvements.

Simon Bischof and Clark, Hurd and Clayton in England; Daimler of Deutz on the Rhine, Riker and Wiegand of the United States, and others, have made improvements in the Otto system.

Ammoniacal gas engines have been successfully invented. _Aqua ammonia_ is placed in a generator in which it is heated. The heat separates the ammonia gas from the water, and the gas is then used to operate a suitable engine. The exhaust gas is cooled, pa.s.sed into the previously weakened solution, reabsorbed and returned to the generator. In 1890 Charles Tellier of France patented an ammoniacal engine, also means for utilising solar heat and exhaust steam for the same purpose; and in the same year De Susini, also of France, patented an engine operated by the vapour of ether; A. n.o.bel, another Frenchman, in 1894, patented a machine for propelling torpedoes and other explosive missiles, and for controlling the course of balloons, the motive power of which is a gas developed in a closed reservoir by the chemical reaction of metallic sodium or pota.s.sium in a solution of ammonia. These vapour engines are used for vapour launches, bicycles and automobiles.

In 1851 the ideas of Huygens and Papin of two hundred years before were revived by W. M. Storm, who in that year took out a gunpowder engine patent in the United States, in which the air was compressed by the explosions of small charges of gunpowder. About fifteen other patents have been taken out in America since that time for such engines. In some the engines are fed by cartridges which are exploded by pulling a trigger.

As to gas and vapor engines generally, it may now be said, in comparison with steam, that although the steam engine is now regarded as almost perfect in operation, and that it can be started and stopped and otherwise controlled quietly, smoothly, instantaneously, and in the most uniform and satisfactory manner, yet there is the comparatively long delay in generating the steam in the boiler, and the loss of heat and power as it is conducted in pipes to the working cylinder, resulting in the utilisation of only ten per cent of the actual power generated, whereas gas and vapour engines utilise twenty-five per cent of the power generated, and the flame and explosions are now as easily and noiselessly controlled as the flow of oil or water. The world is coming to agree with Prof. Fleeming Jenkins that "Gas engines will ultimately supplant the steam."

The smoke and cinder nuisance with them has been solved.

The sister invention of the gas engine is the air engine. There can be no doubt about the success of this busy body, as it is now a swift and successful motor in a thousand different fields. Machines in which air, either hot or cold, is used in place of steam as the moving power to drive a piston, or to be driven by a piston, are known generally as air, caloric, or hot-air engines, air compressors, or compressed air engines, and are also cla.s.sed as pneumatic machines, air brakes, or pumps. They are now specifically known by the name of the purpose to which they are applied, as air ship, ventilator, air brake, fan blower, air pistol, air spring, etc.

The attention of inventors was directed towards compressed and heated air as a motor as soon as steam became a known and efficient servant; but the most important and the only successful air machine existing prior to this century was the air pump, invented by Guericke in 1650, and subsequently perfected by Robert Boyle and others. The original pump and the Magdeburg hemispheres are still preserved.

It is recorded that Amontons of France, in 1699, had an atmospheric fire wheel or air engine in which a heated column of air was made to drive a wheel.

It has already been noted what Papin (1680-1690) proposed and did in steam. His last published work was a Latin essay upon a new system for raising water by the action of fire, published in 1707.

The action of confined and compressed steam and gases, and air, is so nearly the same in the machines in which they const.i.tute the motive power that the history, development, construction, and operation of the machines of one cla.s.s are closely interwoven with those of the others.

Taking advantage of what had been taught them by Watt and others as to steam and steam engines, and of the principles and laws of gases as expounded by Boyle, Mariotte, Dalton, and Gay-Lussac, that many of the gases, such as air, preserve a permanent expansive gaseous form under all degrees of temperature and compression to which they had as yet been subjected, that when compressed and released they will expand, and exert a pressure in the contrary direction until the gas and outside atmospheric pressure are in equilibrium, that this compressed gas pressure is equal, and transmitted equally in all directions, and that the weight of a column of air resting on every horizontal square inch at the sea level is very nearly 14.6 pounds, the inventors of the nineteenth century were enabled by this supreme illumination to enter with confidence into that work of mechanical contrivances which has rendered the age so marvellous.

It was natural that in the first development of mechanical appliances they should be devoted to those pursuits in which men had the greatest practical interest. Thus as to steam it was first applied to the raising of water from mines and then to road vehicles. And so in 1800 Thos.

Parkinson of England invented and patented an "hydrostatic engine or machine for the purpose of drawing beer or any other liquid out of a cellar or vault in a public house, which is likewise intended to be applied for raising water out of mines, ships or wells. By the use of a sort of an air pump he maintained an air pressure on the beer in an air-tight cask situated in the cellar, which was connected with pipes having air-tight valves, with the upper floor. The liquid was forced from the cellar by the air pressure, and when turned off, the air pressure was resumed in the cask, which "preserved the beer from being thrown into a state of flatness." Substantially the same device in principle has been reinvented and incorporated in patents numerous times since.

In the innumerable applications of the pneumatic machines and air tools of the century, especially of air-compressing devices, to the daily uses of life, we may, by turning first to our home, find its inner and outer walls painted by a pneumatic paint-spraying machine, for such have been made that will coat forty-six thousand square feet of surface in six hours; and it is said that paint can be thus applied not only more quickly, but more thoroughly and durably than by the old process. The periodical and fascinating practice of house cleaning is now greatly facilitated by an air brush having a pipe with a thin wide end in which are numerous perforations, and through which the air is forced by a little pump, and with which apparatus a far more efficient cleaning effect upon carpets, mattresses, curtains, clothes, and furniture can be obtained than by the time-honoured broom and duster.

Is the home uncomfortable by reason of heat and summer insects? A compressor having tanks or cisterns in the cellar filled with cool or cold air may be set to work to reduce the temperature of the house and fan the inmates with a refreshing breeze.

Air engines have been invented which can be used to either heat or cool the air, or do one or the other automatically. The heating when wanted is by fuel in a furnace forced up by a working cylinder, and the cooling by the circulation of water around small, thin copper tubes through which the air pa.s.ses to the cylinder.

Do the chimes of the distant church bells lead one to the house of worship? The worshipper goes with the comforting a.s.surance that the chimes which send forth such sweet harmonies are operated not by toiling, sweating men at ropes, but by a musician who plays as upon an organ, and works the keys, valves and stops by the aid of compressed air, and sometimes by the additional help of electricity.

Mention has already been made of office and other elevators, in which compressed air is an important factor in operating the same and for preventing accidents.

If a waterfall is convenient, air is compressed by the body of descending water, and used to ventilate tunnels, and deep shafts and mines, or drive the drills or other tools.

The pneumatic mail tube despatch system, by which letters, parcels, etc., are sent from place to place by the force of atmospheric pressure in an air-exhausted tube, is a decidedly modern invention, unknown in use even by those who are still children. Tubes as large as eight inches in diameter are now in use in which cartridge boxes are placed, each holding six hundred or more letters, and when the air is exhausted the cartridge is forced through the tubes to the distance sometimes of three miles and more in a few minutes.

In travelling by rail the train is now guided in starting or in stopping on to the right track, which may be one out of forty or fifty, by a pneumatic switch, the switches for the whole number of tracks being under the control of a single operator. The fast-moving train is stopped by an air brake, and the locomotive bell is rung by touching an air cylinder. The "baggage smashing," a custom more honoured in the breach than in the observance, is prevented by a pneumatic baggage arrangement consisting of an air-containing cylinder, and an arm on which to place the baggage, and which arm is then quickly raised by the cylinder piston and is automatically swung around by a cam action carrying the baggage out of or into the car.

Bridge building has been so facilitated by the use of pneumatic machines for raising heavy loads of stone and iron, and for riveting and hammering, and other air tools, aided by the development in the art of quick transportation, that a firm of bridge builders in America can build a splendid bridge in Africa within a hundred days after the contract has been entered upon.

Ship building is hastened by these same air drilling and riveting machines.

The propelling of cars, road vehicles, boats, balloons, and even ships, by explosive gases and compressed air is an extensive art in itself, yet still in its infancy, and will be more fully described in the chapter on carrying machines.

The realm of Art has received a notable advancement by the use of a little blow-pipe or atomiser by which the pigments forming the background on beautiful vases are blown with just that graduated force desired by the operator to produce the most exquisitely smooth and blended effects, while the varying colours are made to melt imperceptibly into one another as delicately as the mingled shade and coloured sunlight fall on a forest brook.

But to enumerate the industrial arts to which air and other pneumatic machines have been adapted would be to catalogue them all. Mention is made of others in chapters in which those special arts are treated.

CHAPTER XIII.