only producer that makes gas for gas engines at present is the Dawson,
and in it anthracite is used, because of the difficulty of getting rid
of the tar coming from the Siemens and Wilson producers, using any
ordinary slack.

When this difficulty has been overcome, and that it will be overcome there
can be no manner of doubt, gas engines will rapidly displace the steam
engine, because a gas engine with a gas producer, producing gas from any
ordinary coal with the same ease as steam is produced from a boiler, will
be much safer, and will use one-half the fuel of the very best steam
engines for equal power. The first cost also will not be greater than that
of steam. The engine itself will be more expensive than a steam engine of
equal power, but the gas producer will be less expensive than the boiler
at present. Perfect as the gas engine now is, considered as a machine for
converting heat into work, the possibility of great development is not yet
exhausted. Its economy may be increased two or even three fold; in this
lies the brilliant future before it. The steam engine is nearly as perfect
as it can be made; it approaches very nearly the possibility of its
theory. Its defect does not lie in its mechanism, but in the very
properties of water and steam itself. The loss of heat which takes place
in converting liquid water into gaseous steam is so great that by far the
greater portion of the heat given out by the fuel passes away either in
the condenser or the exhaust of a steam engine; but a small proportion of
the heat is converted into work.

The very best steam engines convert about 11 per cent. of the heat given
them into useful work, the remaining 89 per cent. being wasted,
principally in the exhaust of the engine.

Gas engines now convert 20 per cent. of the heat given to them into work,