Most of the devices for drying steam come under this head.  Such are those in which the steam with the water in suspension is forced to take a circular path, by which the water is hurled by centrifugal force against the concave side of the passage and passes back to the water in the boiler.

SPEED.—­The centrifugal force of a revolving particle varies, as we have seen, as the square of the angular velocity, so that the effort has been to obtain as high a number of revolutions per minute as was consistent with safety and with the principle of the machine.  For example, creamers which are small and light make 4,000 revolutions per minute, though the latest styles run much more slowly.  Driers and sugar machines vary from 600 to 2,000, while on the other hand the necessity of keeping the mercury from hurling off in an amalgamator prevents its turning more rapidly than sixty or eighty times a minute.

However, speed in another sense, the speed with which the operation is performed, is what especially characterizes centrifugal extractors.  In this particular a contrast between the old methods and the new is impressive.  Under the action of gravity, cream rises to the milk’s surface, but compare the hours necessary for this to the almost instantaneous separation in a centrifugal creamer.  The sugar manufacturer trusted to gravity to drain the sirup from his crystals, but the operation was long and at best imperfect.  An average sugar centrifugal will separate 600 pounds of magma perfectly in three minutes.  Gold quartz which formerly could not pay for its mining is now making its owners’ fortunes.  It is boasted by a Southern company that whereas they were by old methods making twenty-five cents per ton of gold quartz, they now by the use of the latest amalgamator make twenty-five dollars.  Centrifugal force, as applied in extractors, has opened up new industries and enlarged old ones, has lowered prices and added to our comforts, and centrifugal extractors may well command, as they do, the admiration of all as wonderful examples of the way in which this busy age economizes time.

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A NEW TYPE OF RAILWAY CAR.

[Illustration:  Fig. 1.—­CAR WITH LATERAL PASSAGEWAYS.]

Figs. 1 and 2 give a perspective view and plan of a new style of car recently adopted by the Bone-Guelma Railroad Company, and which has isolated compartments opening upon a lateral passageway.  In this arrangement, which is due to Mr. Desgranges, the lateral passageway does not extend all along one side of the car, but passes through the center of the latter and then runs along the opposite side so as to form a letter S. The car consists in reality of two boxes connected beneath the transverse passageway, but having a continuous roof and flooring.  The two ends are provided with platforms that are reached by means of steps, and that permit one to enter the corresponding half