Class I. includes also centrifugals for the following purposes:  The removal of must from the grape after crushing, making butter, extracting oils from solid fats, separating the liquid and solid parts of sewerage, drying hides, skins, spent tan and the like, drying coils of wire.

HORIZONTAL CENTRIFUGALS.—­Only vertical machines have been and will be dealt with.  Horizontal centrifugals, that is, those whose spindles are horizontal have been made, but the great inconvenience of charging and discharging connected with them has occasioned their disuse; though in other respects for liquids they are quite as good as vertical separators.  Their underlying theory is practically the same as that hereinbefore discussed.

CLASS II., CREAMERS.—­Centrifugals of the second class separate liquids from liquids.  There are two main applications in this class—­to separate cream from milk and fusel oil from alcoholic liquors.  When a liquid is to be separated from a liquid, the receptacle must be imperforate.  The components of different specific gravity become arranged in distinct concentric cylindrical strata in the basket, and must be conducted away separately.  In creamers the particles of cream must not be broken or subjected to any concussion, as partial churning is caused and the cream will, in consequence, sour more rapidly.

The chief cause of oscillations in machines of this class, where the charge is liquid, is the waves which form on the inner surface.  They may be met by allowing a slight overflow over the inner edge of the rim of the basket; or by having either horizontal partitions, or vertical, radial ones, special cases of which will be noticed.  Oscillations may also be met in the same manner as in sugar machines, by allowing the revolving parts to revolve about an axis through their common center of gravity. (Pat. 360,342—­J.  Evans.)

The crudest form of creamer contains a number of bottles, with their necks all directed toward the spindle, filled with milk.  The necks, in which the cream collects, are graduated to tell when the operation is complete.

Many methods for introducing the milk into creamers have been devised.  It may run in from the top at the center, or emerge from a pipe at the bottom of the basket; or the spindle may be hollow and the milk sucked up through it from a basin below.  It is usual to let the milk enter under hydrostatic pressure (Pat. 239,900—­D.  M. Weston) and let the force of expulsion of the cream be dependent on this pressure.  This renders the escape quiet, and prevents churning.  Gravity, too, is made effective in carrying the constituents off.

The cream may escape through a passage in the bottom at the center, and the skim milk at the lower outer corner; or by ingeniously managed passages both may escape at or near center.  The rate of discharge can be managed by regulating the size of opening of exit passages.