heavy solid impurities which may be in suspension. See Fig. 33. The air
enters the passage, B (if it has no considerable velocity of itself, it
must be forced in), forms a whirlpool in the conically shaped
receptable, A, and passes up out of the passage, D. The heavy particles
are thrown on the sides and collect there and fall through opening, C,
into some closed receiver.

[Illustration: Fig. 33]

CLASS V., GASES AND LIQUIDS.--The occluded gases in steel and other
metal castings, if not separated, render the castings more or less
porous. This separation is effected by subjecting the molten metal to
the action of centrifugal force under exclusion of air, producing not
only the most minute division of the particles, but also a vacuum, both
favorable conditions for obtaining a dense metal casting.

Most of the devices for drying steam come under this head. Such are
those in which the steam with the water in suspension is forced to take
a circular path, by which the water is hurled by centrifugal force
against the concave side of the passage and passes back to the water in
the boiler.

SPEED.--The centrifugal force of a revolving particle varies, as we
have seen, as the square of the angular velocity, so that the effort
has been to obtain as high a number of revolutions per minute as was
consistent with safety and with the principle of the machine. For
example, creamers which are small and light make 4,000 revolutions per
minute, though the latest styles run much more slowly. Driers and sugar
machines vary from 600 to 2,000, while on the other hand the necessity
of keeping the mercury from hurling off in an amalgamator prevents its