consumption of gas is even greater than the Lenoir, being 110 cubic feet
per horse power per hour, as tested with a half-horse engine at a late
exhibition of gas apparatus at Stockport.

So large a consumption of gas prevented these engines coming into extended
use for engines of moderate power, and led inventors to work to obtain
better results. The force generated by the explosion of a mixture of gas
and air is very short lived, and if it is to be fully utilized must be
used quickly; a high pressure is produced, but it very quickly disappears.

The quicker the piston moves after the maximum pressure is reached, the
less will be the loss of heat to the sides of the cylinder. The flame
which fills the cylinder and causes the increase of pressure rapidly loses
heat, and the pressure falls.

The idea of using a free piston was proposed as a remedy; it was thought
that a piston connected to a crank in the ordinary manner could not move
fast enough to utilize the pressure before it was lost. Many inventors
proposed to perform work upon a piston free from any direct connection
with the crank or shaft of the engine; the explosion after attaining its
maximum pressure expends its force in giving velocity to a piston; the
velocity so acquired carries it on against atmospheric pressure until the
energy is all absorbed, and a vacuum or deficit of pressure exists in the
cylinder instead of an excess of pressure. The return stroke is
accomplished by the atmospheric pressure, and the work is now done upon
the engine shaft on the return only. The method of connecting on the
return stroke while leaving the piston free on the out stroke varies, but
in many engines the principle was the same.

Barsante and Matteucci, year 1857, British patent No. 1,625, describe the