"amalgamator." The last invention (Pat. 355,958, White) consists
essentially of a pan, a meridian section of which would give a curve
whose normal at any point is in the direction of the resultant of the
centrifugal force at that point and gravity. There is a cover to this
pan whose convexity almost fits the concavity of the pan, leaving a
space of about an inch between. Crushed ore with water is admitted at
the center between the cover and the pan, and is driven by centrifugal
force through a mass of mercury (which occupies part of this space
between the two) and out over the edge of the pan. The particles of
metal coming in contact with the mercury amalgamate, and as the speed
is regulated so that it is never great enough to hurl the mercury out,
nothing but sand, water, etc., escape. There have been many different
constructions devised, but this general principle runs through all. By
having annular flanges running down from the cover with openings placed
alternately, the mixture is compelled to follow a tortuous course, thus
giving time for all the gold or other metal to become amalgamated.
There are ridges in the pan, too, against which the amalgam lodges. It
is claimed for this machine that not a particle of the precious metal
is lost, and experiments seem to uphold the claim.

A machine for separating fine from coarse clay for porcelain or for
separating the finer quality of plumbago from the coarser for lead
pencils uses an imperforate basket, against the wall of which the
coarser part banks and catches under the rim. The finer part forms an
inner cylindrical stratum, but is allowed to spill over the edge of the
rim. The mixture is introduced at the bottom of the basket at the
center.

CLASS IV., GASES AND SOLIDS.--There is a very simple contrivance
illustrating machines of this class used to free air from dust or other
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 m