Combined Simplex Engine and Buire-Lencauchez Gas-producer 124 49-50. Bénier Engine and Gas Plant (sectional plan and elevation) _face p._ 127 51. Section of Simplex Gas-producing Plant 135 52. Agricultural Oil Locomotive 137 GAS AND PETROLEUM ENGINES CHAPTER I HISTORY OF THE GAS ENGINE The history of gas engines may be said to date from a time when coal gas and petroleum were unknown. This statement appears at first somewhat paradoxical, but it arises from the fact that the first gas engine, invented by the Abbé de Hautefeuille in 1678, used the explosive force of gunpowder as a motive power. The principle of this early gas engine, however, is exactly the same as that of its more modern brothers; that is, the work is done by the expansion and cooling of a volume of heated gas, the only difference being that gunpowder contains within its grains the oxygen necessary for its combustion, while coal gas or petroleum require admixture with the oxygen of the air before they can be made to explode. Two years after the Abbé de Hautefeuille had made public his idea, in a memoir entitled _A Method of Raising Water by means of Gunpowder_, the Dutch savant Huyghens published a similar work, describing an apparatus consisting of a cylinder with two leather exhaust pipes, forming valves; to the bottom of the cylinder was screwed a small box in which gunpowder was to be ignited. The effect of the explosion was to drive out a large quantity of heated gas through the valves, which closed again when it had passed. The gas remaining in the cylinder soon cooled down, so that the pressure within it fell below that of the surrounding atmosphere, and caused the piston to be forced down by the excess of atmospheric pressure.