Does not the expenditure of oil in large motors largely offset the
saving in coal? And then, gas motors are sold at high prices, as are gas
generators, and this installation necessarily requires the addition of a
large gasometer, scrubbers, etc. The wear of these apparatus is rapid,
and if we take into account the interest and amortization of the capital
engaged, we shall find that the use of steam is still more economical.
The obstruction caused by bulky apparatus is another inconvenience, upon
which it is unnecessary to dwell. In a word, the question is a very
complex one. We look at but one side of it in occupying ourselves only
with the coal consumed, and we shall certainly expose those who allowed
themselves to be influenced by the seductive figures of consumption to
bitter disappointment.

To answer such objections Mr. Aimé Witz has established a complete
parallel between the two systems, in which he looks at the question from
a theoretical and practical and scientific and financial point of view.
Considered as a transformation apparatus, a steam motor burning good
Cardiff coal in a Galloway boiler with feed water heaters will consume
(with a good condensing engine utilizing an expansion of a sixth) from
1,100 to 1,250 grammes of coal per effective horse hour, which
corresponds to a rough coefficient of utilization of 9.7 per cent. A gas
generator supplying a gas motor burning Swansea anthracite and Noeux
coke, medium quality, will consume 516 grammes of anthracite and 90 of
coke to produce 2,370 liters of gas giving 1,487 heat units per cubic
meter. Of the 3,524 heat units furnished to the motor by the 2,370
liters of gas, the motor will convert 18 per cent. into disposable
mechanical work.

With the boiler, the gross rendering of the whole is 7 per cent. With