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 spindle, the point of which takes the weight, so that the
turbine becomes a top which can be kept spinning as long as the steam
supply lasts.
These toys, for such they must be considered, are very easy to make, and
are "warranted to give satisfaction" if the following instructions are
carried out.
A Small Top.--Fig. 74 shows a small specimen, which is of the
self-contained order, the boiler serving as support for the top.
[Illustration: FIG. 74.-Simplest form of steam top.] [1]
[Footnote 1: Spirit lamp shown for heating boiler.]
For the boiler use a piece of brass tubing 4 inches or so in diameter and 3
inches long. (The case of an old brass "drum" clock, which may be bought
for a few pence at a watchmaker's, serves very well if the small screw
holes are soldered over.) The ends should be of brass or zinc, the one
which will be uppermost being at least 1/16 inch thick.
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