h a small twist drill of the proper
size.

A brass elbow, which may be purchased for a few pence, should be driven
into the waste hole, and a small shield be nailed under the air hole. A
couple of screwed-on cross pieces are required to steady the motor sideways
and raise the elbow clear of the ground.

The motor may be geared direct to a very small dynamo, if the latter is
designed to run at high speeds. If a geared-down drive is needed, a small
pulley--such as is used for blinds, and may be bought for a penny--should
be attached to the shaft, and a bootlace be employed as belt. Avoid
overloading the wheel, for if it is unable to run at a high speed it will
prove inefficient.

[Illustration: FIG. l08.-Water motor working a photographic dish-rocker.]

Lubrication.--The water will keep the bearings cool, but the bearings
should be well lubricated. The most convenient method of effecting this is
to bore holes in the bearings, and from them run small pipes to an oil
reservoir on the top of the case (as in Fig. 70), where they are fed on the
siphon principle through strands of worsted.

Alternative Construction.--If an all-metal case is preferred, the reader
might utilize the description given of a steam turbine on pp. 170-178. The
details there given will apply to water as well as steam, the one exception
being that a nozzle of the kind described above must be substituted for the
steam pipe and small ports.

XXII. MODEL PUMPS.

Every steam boiler which has to run for long periods and evaporate
considerable quantities of water should be in connection with a pump
capable of forcing water in against the highest pressure used. On a
previous page (p. 158) we have described a force pump driven directly off
the crank shaft of an engine. As the action of this is dependent on the
running of the engine, it is advisable, in cases where the boiler may have
to work an engine not provided with a pump of its own, to install an
independent auxiliary pump operated by hand or by steam, and of
considerable capacity, so that in an emergency water may be supplied
quickly.

[Illustration: FIG. l09.-Vertical section of force pump.]

Making a Hand pump.--Fig. 109 shows the details of a hand pump which is
easy to make. The barrel is a length of brass tubing; the plunger a piece
of brass or preferably gun-metal rod, which fits the tube closely, but
works easily in it. The gland at the top of the barrel, E, is composed of a
piece, D,