Fig. 31 (Pat. 355,050—­C.A.  Backstrom) shows another very late style of creamer.  A pipe delivers the milk into P^{4}.  Passing out of the tube separation takes place, and cream falls down the center to P^{2} and out of O^{3}.  When the compartment under the first shelf becomes full of the skim milk, the latter passes up through the slot, S, strikes a radial partition, R, and its course is reversed.  Here more cream separates and passes to center and falls directly, and so on through the whole series of annular compartments, until the top one, when the skim milk enters tube T^{2} and passes out of O^{2}.  By this operation there are substantially repeated subjections of specified quantities of milk to the action of centrifugal force, bringing about a thorough separation.  By changing the course of the milk in direction, its path is made longer.  This machine can run at much lower speed than many other styles, and yet do the same work.

[Illustration:  Fig. 31]

CLASS III., SOLIDS FROM SOLIDS.—­As for grain machines, which are in this class, it may be said that in centrifugal flour bolters, bran cleaners, and middlings purifiers, though theoretically centrifugal force plays an important part in their action, yet practically the real separation is brought about by other agencies:  in some by brushes which rub the finer particles through wire netting as they rotate against it.

The principle exhibited in a separator of grains and seeds is very neat. (Pat. 167,297.) See Fig. 32.  That part of the machine with which we have to do consists essentially of a horizontal revolving disk.  The mixed grains are cast on this disk, pass to the edge, and are hurled off at a tangent.  Suppose at A. Each particle is immediately acted on by three forces.  For all particles of the same size and having the same velocity the resistance of the air may be taken the same, that is, proportional to the area presented.  The acceleration of gravity is the same; but the inertia of the heavier grain is greater.  The resultant of the two conspiring forces R and (M_v_^{2})/2 varies, and is greater for a heavier grain.  Therefore, the paths described in the air will vary, especially in length; and how this is utilized the drawing illustrates.

[Illustration:  Fig. 32.]

ORE.—­In ore machines there is one for pulverizing and separating coal (Pat. 306,544), in which there is a breaker provided with helical blades or paddles, partaking of rapid rotary motion within a stationary cylinder of wire netting.  The dust, constituting the valuable part of the product, is hurled out as fast as formed.  In this style of machine, beaters are necessary not only for pulverizing, but to get up rotary motion for generating centrifugal force.  In the classes preceding, the friction of the basket sufficed for this latter purpose; but here there is no rotating basket and no definite charge.  As the material falls through the machine, separation takes place.  Various kinds of ore may be treated in the same manner.