A Double Acting Gas Engine.-In the engines that have gone before you will have observed that the explosive force of the gas acted on one side of

the piston only, and that is the way that all of the gas, gasoline, and oil engines are made to-day.

In 1797 a Frenchman named Lebon took out a patent for a double acting gas engine in which the explosive fuel mixture was compressed by a com

pression pump and then admitted alternately on each side of the piston as steam is in an ordinary steam engine.

The piston rod was connected with a shaft and this worked the gas compressor pump. To fire the fuel mixture Lebon intended to use a spark set up by an electric machine which would also be driven by the shaft. Unfortunately the inventor was assassinated in 1804 and so his engine came to naught.

FIG. 4. BARNETT'S IMPROVED IGNITER

The Gas Engine Competes With the Steam Engine. The first gas engine to be put to the practical test of pumping water was made by Samuel Brown, of London, in 1823. Like Hautefeuille's gas engine, his was of the vacuum type, and in the next ten years four of these engines were used in England for pumping water. Each engine could raise 300 gallons of water 15 feet high on 1 cubic foot of gas.

The Invention of an Improved Igniter.-William Barnett, also of England, got up in 1838 a double acting gas engine, but his fame rests on an ignition cock for firing the fuel mixture.

In this igniter, see Fig. 4, which was screwed to the head of the cylinder, two flames were used, one

GAS

AIR INLET.

AND EXHAUST

DISCHARGE

ELECTRIC
SPARK

FIG. 5. BARSANTI AND MATTEUCCI'S ELECTRIC SPARK IGNITER

on the inside and the other on the outside of the cylinder; now when the force of the explosion put out the inside flame, a valve opened in the cock and it was again relit by the outside flame, which was always burning.

Then Came the Electric Spark.-It was Barsanti and Matteucci, of Italy, who first used the electric spark to ignite the fuel charge in the cylinder. This

was in 1857, when electricity was getting pretty well out of its swaddling clothes. Their engine was also of special design, but it was not used afterward, and hence did not help along the state of the art. Fig. 5 shows their igniter.

The Advent of the Commercial Gas Engine.—The workers along the line of the gas engine were busy now everywhere, but Lenoir, of France, designed and built, in 1860, the first gas engine that was really a commercial success.

There was nothing new or original about this gas engine of Lenoir's, but what he did was to work out every single part of it so carefully that when he built the engine it worked efficiently. His engine was very like the steam engine as it is built to-day, but, of course, with the addition of valves to admit the fuel mixture, and others to let the burnt gases escape. It is shown in Fig. 6.

In 1860 two of Lenoir's engines were built in Paris, one of six and the other of twenty horse power. According to descriptions published at that time both of these engines ran as smoothly and as silently as the best steam engines then in use.

An American Gasoline and Oil Engine.—In 1873 George Brayton began to build in the United States gasoline and oil engines which were better than any that had yet been produced.

The outstanding feature of the design of his engines was that the fuel mixture burned at a constant pressure instead of in a series of explosions.

The air was compressed in a cylinder by a piston which was connected to the beam of the engine, and this was admitted to the power cylinder together with a small quantity of oil on the upstroke of the piston in the compression cylinder. As the fuel mixture passed into the power cylinder it was ig

nited by a flame and thus the pressure was kept

constant.

To prevent the fuel mixture from backfiring from the power cylinder into the compression cylinder a piece of wire gauze1 was placed in the intake pipe between them. As gas did not work well in Bray

1If a piece of wire gauze is placed over a Bunsen burner the flame may be lighted either above or below the gauze but it will not pass through it. This is because the wires of the gauze are very good conductors of heat and prevent the gas on the other side from getting hot enough to light.