An “ore concentrator” (Pat. 254,123), as it is called, consists of a pan having rotary and oscillatory motions.  Crushed ore is delivered over the edge in water.  The heavy particles of the metal are thrown by centrifugal force against the rim of the pan, overcoming the force of the water, which carries the sand and other impurities in toward the center and away.

AMALGAMATORS.—­The best ore centrifugal or separator is what is called an “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 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.