that it is cheaper, and quite as satisfactory, to use a built-up
foundation instead, and, if necessary, to cut a trough for the fly-wheel
to run it. This arrangement, however, only obtains where larger engines
are concerned. A half-compression handle by which the exhaust cam is
moved laterally on the side shaft as required is not needed on very
small engines.

[Illustration: FIG. 1.--General Arrangement of a Gas Engine and
Accessories.]

Further reference will be made to this in another chapter, and,
although this is not a necessity on a _small_ engine, it is always
employed on engines over 2 B.H.P. In fig. 1, HW is the cooling water
outlet and CW the inlet. A small drain cock is shown at DC, through
which the water in the cylinder water-jacket may be drawn off when
required. The pipes leading to the inlet and outlet of this supply are
connected to the cooling water tank by means of a couple of broad, flat
nuts and lead washers, one inside and the other outside the tank, the
latter, when clamped up well, making a perfectly water-tight joint. The
outlet pipe making an acute angle with the side of tank, the washers
used there should be wedge-shape in section. It is also desirable to fit
a stop-cock SC, so that the pipes can be disconnected from the engine
entirely, or the water-jacket emptied without running the whole of the
water out of the tank. The exhaust pipe EP is made up of gas-barrel. It
should lead from the engine to the silencer or exhaust box (if one is
found to be necessary) as directly as possible, _i.e._, with no more
bends than are needed, and what there are should not be acute. The
silencer can be inside or outside the engine-room, whichever is most
convenient; but both it and the exhaust piping should be kept from all
direct contact with wood-work, and at the same time in a readily
accessible position.

Beyond the exhaust-pipe and box and the water-tank, the gas bag GB and
gas meter (where small powers are concerned, the ordinary house or
workshop lighting meter may be used without inconvenience) are the only
other accessories which are included in a small installation.

[Illustration: FIG. 2.--A Section of a Gas Engine.]

Fig. 2 gives a sectional view, showing the cylinder and liner. The
latter is a very desirable feature in any type of gas engine, but
especially in the larger sizes; for at any future time, should it be
found necessary to re-bore the liner, it can be removed with comparative
ease,