and may be conducted away. The
impurities, likewise, after falling down the sides of the receptacle,
are carried off. The advantages of this method are that no filtering
material is needed and the filtering surface is never in contact with
anything but pure liquor.

Very fine sawdust is, to a considerable extent, employed in sugar
refineries as a filtering medium. By such use the sawdust becomes mixed
with sand, fine particles of cane, etc. As sawdust of such fineness is
expensive, it is desirable to purify it in order to reuse it. A
centrifugal (Pat. 353,775--J.V.V. Booraem) built on the following
principle is used for this purpose. It has been observed that by
rotating rather _slowly_ small particles of various substances in
water, the finer particles will be thrown outward and deposit near the
circumference of the vessel, while the heavier and coarser particles
will deposit nearer to or at the center, their centrifugal force not
being sufficient to carry them out. A mere rod, extending radially in
both directions, serves by its rotation to set the water in motion.

Another form of filter of this second kind (Pat. 148,513) has a
rotating imperforate basket into which the impure liquor is run. Within
and concentric with it is another cylinder whose walls are of some
filtering medium. The liquid already partly purified by centrifugal
force passes through into the inner cylinder, thus becoming further
purified. Centrifugal filters are used also to cleanse gums for
varnishes.

HONEY.--The simplest form of honey extractor (Pat. 61,216) consists of
a square framework, symmetrical with respect to a vertical spindle.
This framework is surrounded by a wire gauze. The combs, after having
the heads of the cells cut off, are placed in comb-holders against the
wire netting on the four sides, the cells pointing outward. The machine
is turned by hand. The honey is hurled against the walls of a receiving
case and caught below. But few improvements have been made on this. The
latest machines are still hand-driven, as a sufficiently high velocity
can be obtained in this manner. In one style the combs are placed upon
a floor which rests upon springs. The rotating box is given a slight
vertical and horizontal reciprocatory motion, by which the combs are
made to grate on the wire gauze sides, breaking the cells and
liberating the honey. Thus the labor of cutting the cells is saved.
Every comb has two sides, and to present each side in