GAS-ENGINE. Many attempts have been made to utilize, as a motive-power, the expansive force arising from the explosion of a mixture of common coal-gas, such as is iu general use for illuminating purposes, and common air. The first atempt of this kind which had any commercial success was that of Lenoir, a French inventor. It resembles in its general features an ordinary horizontal steam-engine. It has two slides, one on each side of the cylinder, which are opened and closed by eccentrics in the usual way. Through one of the slides, air and gas flow into the cylinder, in the proportions of about 11 of air to 1 of gas, until the cylinder is pearly half full, when the connection with the galvanic battery is made by the revolution of the shaft, caasiug a spark inside the cylinder, and consequent explosion of the mixture of air and gas. This explosion forces the piston from the middle of the cylinder to the further end. The products of the escape front the cylinder by the other slide-valve, which opens at the proper instant. The momentum which the fly-wheel has now acquired the piston back to the middle of the cylinder, sucking in behind it, through openings, which are made by the action of the eccentric on the slide, a fresh supply of air and gas; and when the piston has reached to the middle of the cylinder, the further inflow of air and gas is stopped by the slide closing, and at the same instant a spark of electricity is sent into the air and gas, exploding it as before. The first half of the stroke of the piston is thus employed ill sucking in the requisite quantities of air and gas, and the last half of the stroke giving off the power arising from the explosion of the mixture of air and gas. Better gas-engines than Lenoir's are now in use, and one of the best is styled the "Otto" silent gas-engine. In several respects it resembles Lenoir's, but it differs from it in others.
Instead of an electric spark, a small constantly burning gas flame is used to firethe charge. But the main difference lies in the use of a more dilute mixture of gas and air, placed under a pressure of about 30 lbs. above the atmosphere, by which only a portion of the charge becomes combustible; the remainder is simply expanded. and so not only is the shock of a full explosion avoided, but there is a more sustained pressure on the piston throughout the stroke. In default of a diagram, we may compare the interior of the cylinder to that of a soda•water bottle with straight sides lengthwise, only it has no constricted portion or neck. One third of its length at the bottom end is taken up by the combustion chamber; another third by the piston; and the remaining third or rather more by the space over which the piston travels. A jacket of cold water sur rounds the cylinder to keep it cool. There are two openings in the combustion chamber —one for the admission of the charge, and the other for the escape of the products of combustion. Attached to the combustion chamber there is a slide-valve whose move ments are so arranged that it first admits the air and gas in due proportions, which the return of the piston compresses, and then another movement of the valve fires the mix ture by exposing it to the gas-flame. The explosion, so to call it, occurs once in two revolutions when the engine is fully loaded, but less often when it is not. In the Otto it acts on the piston at the beginning, not as in the Lenoir at the middle of the stroke; but the piston is connected in a similar way with the fly-wheel, in both engines. The cost.for gas is about one penny per hour per horse-power.