rapidity of the side shake, and the supply of clear water at the head. Having adjusted these three conditions to a given feed delivered on the belt, that feed should remain constant, and the result, both in the richness of mineral collected and in the poverty of the tailings, will be continuously maintained.

The countershaft to drive the Frue concentrators is placed parallel with the cam shaft and main line shaft of the mill, and is, therefore, at right angles to the crank shaft and pulley of the vanner. This necessitates the use of a quarter-twist belt, and the proper placing of this countershaft is very important, for with it properly set, the quarter-twist belt runs as well, as true, and with as little wear as if it were a straight belt; while if not properly set, it will run off the pulley.

As this is not generally understood, even by good mechanics, the accompanying cut is given to illustrate the placing of this countershaft; a a is the crank shaft of the concentration; b b is the countershaft; on b b are one tight and one loose pulley; the belt is shown on the tight pulley. The crank shaft is not horizontal. The rule is as follows: "In placing the countershaft and its pulley, the pulley should be set so that the side from which the belt leaves it is in line with the square of the crank shaft of the concentrator at that point."

The Embrey concentrator is similar in most respects to the Frue vanner, differing chiefly in the direction of the shake, which is longitudinal. Not many of them have been put in use in California, as the Frue Company owns the Embrey patent, and believing the vanner to be the best machine, they have not pushed the Embrey.

Two forms of the Embrey machine are made, one compact in form, with crank shaft passing under the shaking frame, and supporting, by the latter, the whole weight of the belt and two underhanging rollers. This form is in fact identical with the vanner, except that the crank shaft is placed at right angles to the length of the belt, instead of parallel to same, and it is made with iron or wood frame, as preferred.

The second form, and the one most desirable for economy in running, is arranged with the driving shaft at the lower end of shafting frame, so that while running all parts can be regulated, and any play taken up, and the shaking frame does not carry the hanging rollers, which are supported by the main frame, and carry about one half of the main belt. The shaking frame and mechanism is thus relieved of the weight of the two lower rollers, and nearly one half of the weight of the heavy belt, an important. point, considering the high speed necessary on the end shake machine.

The only advantage of the first form over the second is in saving a little floor space for the same length of working belt.

The advantages of the second form are in reduced power required, reduced wear and tear, and greater accessibility of working parts while in motion.

A

The accompanying cuts show the two forms of the Embrey, as they were made some time ago. Since they were engraved several improvements have been made, but time did not permit later cuts to be made. few of the improvements consist in mechanism, for regulation of the progressive motion from in front of the machine; and the carrying or shaking frame is now supported from below, in the wooden frame machine, and not from above, as in the cut. Silvered copper plates on the ore distributor are used, when needed, to save amalgam.

If on the same belt both end and side shake mechanism be applied alternately, with the same conditions of feed and speed, it will be found that at a speed of 180 to 200 revolutions per minute, and the ordinary slight inclination of the belt, a perfect separation of clear mineral can be made on most ores with the vanner. If the end shake be substituted now, other conditions being the same, it will be found impossible to keep back the sand from passing over the mineral, even with excessive use of clean water at the head; and a separation can only be accomplished by increasing the speed to 235 or 240 revolutions, and increasing the speed naturally increases the wear and tear very materially.

The Embrey is in use in several mills in Colorado, Montana, the Southern States, etc., and at the Anaconda Copper Mine in Montana, the wooden-frame Embrey is preferred to any other concentrator. One of its patented points is the use of the vibrating water distributor.

The Triumph concentrator (see cut) is very much like the Embrey, which is the earlier machine.

It is a rubber belt, inclined, shaking longitudinally, and revolving slowly. Its crank shaft, like the Embrey, revolves from 235 to 240 times a minute, in order to make the separation of the mineral from the sand. Its main novelty is the use of a friction roller to regulate the forward motion of the belt, instead of a cone pulley, which is used in the vanner and Embrey machines. It has also an amalgam saver, consisting of an iron trough in which turns slowly a horizontal shaft, with stirrers. Quicksilver is kept in this trough. The shaking table is supported on upright springs, and the main frame is of cast-iron. It is a neat looking machine,

and can do good work. Many machines have been sold. It is in use at the Empire Mill (Grass Valley), and is liked.

The Duncan ore concentrator, like the Hendy concentrator, is circular in form, and of iron. Its principle is an ingenious combination of movements, imitating the process of panning by hand. "The agitation resulting from this movement causes the mineral to settle to the bottom around the outside of the pan, where it is held by centrifugal force, until discharged through the gates, while the gangue is held in suspension, and gradually carried by the force of the current to the central discharge. The pan, by this centrifugal motion, making, say eight and a half revolutions per minute, causes the pulp to flow around over its surface to the extent of about three revolutions, or equal to a distance of some thirty feet before it is discharged, thereby giving the sulphurets or other mineral time to settle before the gangue passes off.

"The wrist-pin, on the balance-wheel, is made adjustable, so that the motion of the pan can be varied to adapt it to the requirements of different classes of ore.'

8 mi