he outside
of the casing, and this method has the advantage of giving easy detachment
for alteration or replacement.

Balancing the Wheel.--As the wheel will revolve at very high speed, it
should be balanced as accurately as possible. A simple method of testing is
to rest the ends of the spindle on two carefully levelled straight edges.
If the wheel persists in rolling till it takes up a certain position,
lighten the lower part of the wheel by scraping off solder, or by cutting
away bits of the vanes below the circumference of the disc, or by drilling
holes in the disc itself.

Securing the Wheel.--When the wheel has been finally adjusted relatively
to the nozzle, tighten up all the spindle nuts hard, and drill a hole for a
pin through them and the disc parallel to the spindle, and another through
N3 and the spindle. (Fig. 70.)

Gearing.--The gear wheels should be of good width, not less than 3/16
inch, and the smaller of steel, to withstand prolonged wear. Constant
lubrication is needed, and to this end the cover should make an oil-tight
fit with the casing, so that the bottom of the big pinion may run in oil.
To prevent overfilling, make a plug-hole at the limit level, and fit a
draw-off cock in the bottom of the cover. If oil ducts are bored in the
bearing inside the cover, the splashed oil will lubricate the big pinion
spindle automatically.

[Illustration: FIG. 73.--Perspective view of completed turbine.]

General--The sides of the casing are held against the drum by six screw
bolts on the outside of the drum. The bottom of the sides is flattened as
shown (Fig. 70), and the supports, S1 S2, made of such a length that when
they are screwed down the flattened part is pressed hard against the bed.
The oil box on top of the casing has a pad of cotton wool at the bottom to
regulate the flow of oil to the bearings. Fit a drain pipe to the bottom of
the wheel-case.

Testing.--If your boiler will make steam above its working pressure
faster than the turbine can use it, the nozzle may be enlarged with a
broach until it passes all the steam that can be raised; or a second nozzle
may be fitted on the other end of the diameter on which the first lies.
This second nozzle should have a separate valve, so that it can be shut
off.

XVIL. STEAM TOPS.

A very interesting and novel application of the steam turbine principle is
to substitute for a wheel running in fixed bearings a "free" wheel pivoted
on a vertical spind