Up to recent years there was no reason for putting the question that forms the title of this article, for it was admitted by all that the conversion of thermic energy, or heat produced by the combustion of coal, into mechanical energy or work could no longer be effected economically except by having recourse to steam. In ordinary language, and even to manufacturers, steam engine was the equivalent of thermic motor, and it would not have occurred to any one to use anything else but steam to effect the transformation.

The progress that has been made during the last twenty years in the thermatic study and construction of gas motors (without speaking of hot air motors) has shown that the use of steam is not absolutely indispensable for the production of work, and it has demonstrated that, as regards dynamic product, the gas motor preserves the advantage, although the relatively high price of the illuminating gas employed in the production of the motive power generally renders the use of this combustible more costly than steam, especially for high powers.

The economic truth of twenty years ago, when gas motors absorbed 1,500 liters per horse hour and exceeded with difficulty an effective power of from 8 to 10 horses, has become less and less certain, when the consumption has successively descended to 1,200, 1,000, 800 and even to 600 liters of gas per horse hour, the power of the motors rising gradually to 25, 50 and 100 horses with a motor having a single cylinder of a diameter of 57 centimeters.

The Thermic Motor Of The Future 799 3a

FIG. 1. - CORLISS ENGINE AND BOILER OF 100
INDICATED H.P. - ELEVATION AND PLAN.

A, cylinder; B, condenser; C, boiler; R, feed water heater; D, chimney.

But these results did not suffice, and it was desired to do better still by dispensing with the use of high priced illuminating gas. An endeavor was made to obviate the difficulty by manufacturing a special gas for the motive power, as steam is produced for the same object, by distilling coal, carbureting air, producing water gas by the Dowson process, and by other equivalent processes.

The strides made in this direction were finally crowned with success, and the results obtained in the recent experiments due to Mr. Aimé Witz, an undoubted authority in the matter, permit of affirming that now and hereafter, in many circumstances, a gas generator supplying a gas motor will be able to advantageously dethrone a steam boiler supplying a steam engine of the same power.

These conclusions, which tend to nothing less than to limit the reign of the steam engine, are confirmed on the one hand by an experiment carried on for the last two years in the Barataud flour mill of Marseilles, where a 50 h.p. "Simplex" motor has been running day and night for several months without stopping, and consuming but about 500 grammes of English anthracite per effective horse hour, and, on another hand, by some personal experiments of Mr. Witz's, to which we shall shortly advert, and whence there results a sensibly equivalent production for a motor of 100 indicated h.p., corresponding to a power of 75 effective horses.

Before establishing, with Mr. Witz, a comparison of the two systems in pressure, steam or gas, let us state in a few words in what the latter consists, the steam engine and the boiler that supplies it being so well known that no description is necessary.

The Dowson gas generator does not differ essentially from the numerous generators devised during recent years for the manufacture of gaseous combustibles, the use of which is so often convenient. The motor that it supplies is the most powerful single cylinder one that has hitherto been constructed. It is of 100 indicated h.p., and its normal angular velocity is 100 revolutions per minute. On trial it has yielded 112 indicated h.p., and 76.8 effective h.p., corresponding to an organic rendering of 69 per cent. This motor, elaborated by Messrs. Delamare-Bouteville & Malandin, of Rouen, operates by compression and in four periods, according to the Beau de Rochas cycle. We give the aspect of it in Fig. 3. In the first period the mixture of air and gas is sucked in, in the second it is compressed, in the third it is ignited, and in the fourth the products of combustion are expelled.

The Thermic Motor Of The Future 799 3b

FIG. 2. - SIMPLEX MOTOR, DOWSON GENERATOR OF
100 INDICATED H.P. - ELEVATION AND PLAN.

A, cylinder; B, gas conduit; C, rubber pockets; D. gasometer;
E, purifier; F, scrubber; G, hydraulic main; H, cooling pipe;
I steam injector; K, steam boiler and superheater; L, gas
generator; M, charger; N, discharge of the motor.

Ignition is effected electrically by a series of sparks playing between two platinum points in the slide valve, and this permits of regulating the instant of ignition through the edges of the orifices. The angular velocity is regulated by a Watt's governor, which secures an isochronism of the motion independently of the charge.

The setting in motion of so powerful an engine is effected very easily by means of an arrangement that permits of introducing into the cylinder, while the piston is in the center of the stroke, a mixture of air and gas whose pressure is sufficient at the arrival to expel the inert products. After this the ignition takes place, and the explosion is sufficient to set the motor in motion.

The trials made by Mr. Witz with the motor represented in Fig. 3 gave the following results, deduced from an experiment of 68 hours. The figures relate to one effective horse power, measured with the brake upon the shaft of the motor.

 Consumption of anthracite. 516 grammes.

" " coke. 96 "

Consumption of water for the injection