This last figure will appear very high, but the fact must not be lost
sight of that it is a question of poor gas, the net cost of which varies
between one and two centimes per cubic meter, and the calorific power of
which is but 1,487 heat units per cubic meter of constant volume, and
supposing the steam condensed. This combustion of 612 grammes of
combustible per effective horse hour is remarkable, and fully shows what
may be expected of the gas motor supplied by a gas generator in putting
to profit certain improvements that will hereafter be possible, such,
for example, as the lightening of the movable parts of the motor, the
bettering of its organic rendering (now quite feeble), the use of better
oils, the reduction of the consumption of water, the superheating of the
steam injected into the gas generator, etc.

A well constructed steam engine, carefully kept in repair and as much
improved as it is possible to make it, would certainly consume twice as
much coal to produce the same quantity of effective work, say at least
1,200 grammes per horse hour. But, as has been objected with reason, it
does not suffice to compare the figures as to the consumption of fuel in
order to institute a serious comparison between the steam engine and the
motor using poor gas.

The gas generator requires the use of English anthracite, while a steam
boiler is heated with any kind of coal. The prices of unity of weight
are therefore very different. Moreover, the gas motor necessitates an
immense amount of water for the washing of the gas and the cooling of
the cylinder, through circulation in the jacket. It is well to keep this
fact in view. On another hand, the lubrification of the cylinders
requires a profusion of oil whose flashing point must be at a very high
temperature, else it would burn at every explosion and fill the cylinder
with coom. Such oil is very costly.