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

It is in use at 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

The foregoing is the description given by the manufacturers and owners of the Duncan concentrator. It is well made and many have been sold. Its weight is about 1,750 pounds, and it requires to run it about 4-horse power.

Shaw's disk concentrator and amalgamator is of recent introduction, and its merit therefor is not yet settled. It is described as follows by the inventor (please see cut also):

In this machine there is a circular copper disk in the shape of a very shallow cone, with the apex turned downward, to which an eccentric motion of about one half inch throw is communicated by a vertical spindle, which is geared even to a light horizontal shaft, running from 250 to 300 revolutions per minute. The disk does not revolve, being subject only to the eccentric motion, the result being the panning motion, considered so desirable in all concentrating appliances. At work the pulp is received from the mill in the round pan with a perforated bottom supported over the center, passing in the form of rain onto the vibrating disk; the revolving stirrers keep the pulp active, thus allowing the heavier particles contained therein to percolate to the bottom. Coming in contact with the surface of the disk, they move at once towards the center, where a small screen is provided for their egress. The pulp composed of the worthless sands and water pass over the periphery of the disk and are carried off by means of the circular trough provided for that purpose.

In order to assist or retard the motion of the pulp towards the periphery, a number of revolving radial arms are provided, to which are secured at short intervals small notched stirrers of sheet copper, which dip into the pulp to within about a quarter of an inch of the face of the pan or disk. These revolving stirrers regulate the discharge of the pulp; they are set like wings and can be adjusted at different angles so as to throw the pulp out more or less rapidly as desired.

It can also be used as an amalgamator by replacing the screen in the center by a close fitting plug and quicksilvering the disk, but it is not intended to be used for its double purpose at the same time.

It is claimed to save the sulphurets clean with little loss, and to have capacity from 5 to 8 tons in 24 hours.

GOLDEN GATE SULPHURET CONCENTRATOR.

[From a printed description issued by the company.]

The Golden Gate sulphuret concentrator consists of a tray about eleven feet in length, resting upon a stout iron framework, upon which it has a longitudinally reciprocating movement. This reciprocating movement varies in speed in such manner as to cause the pulp, fed upon the tray at one end, to travel slowly over its surface towards the other end, and the pulp is, by the shaking motion, kept in a loose condition, so that the mineral may settle out of the gangue upon the surface of the tray. The tray proper consists of two distinct parts, forming, however, one continuous surface; one part, being designed for the settling of the mineral, is horizontal, and has hardly any perceptible current of water, thus allowing the fine mineral to settle out of the water and reach the bottom of the tray; the other part has an adjustable inclination upwards from its junction with the horizontal part, and over this part the current of wash water flows, which washes away the gangue from the mineral. At the junction of the horizontal with the inclined part of the tray, and extending across its width, is a "protecting plate," set somewhat above its surface, and parallel thereto. Above the protecting plate is an "exhaust pipe," within which a vacuum, sufficient to sustain a column of four or five inches of water, is constantly maintained by a small exhaust fan. On the lower side of the "exhaust pipe," above the "protecting plate," are openings into which the gangue and water are drawn, by the vacuum maintained, being then discharged over each side of the machine into the waste sluice.

The operation of the sulphuret concentrator is as follows:

The crushed ore, with a suitable amount of water, is fed onto the horizontal part of the tray, through the "distributor" shown at the extreme left of the figure. The peculiar motion communicated to the tray causes the pulp to slowly travel towards the "protecting plate," and at the same time keeps the pulp in a loose condition, allowing the heavier mineral to sink to the bottom, so that, on arriving at the plate, the pulp is separated into distinct layers, with the mineral at the bottom, the heavy gangue above the mineral, and the light gangue and water at the top; the plate having been properly adjusted for the ore, allows all the mineral, with some of the gangue, to pass under it, while the larger part of the gangue, and all the surplus water, pass above the plate, and on arriving at the exhaust pipe, are instantaneously drawn off and discharged over the sides of the tray into the waste sluice. That portion of the pulp which has passed under the plate, now consisting largely of mineral, continues on up the inclined part of the tray, where it can be freed from that part of the gangue which is still mixed with it, by a current of water flowing down from the head of the tray, this gangue and wash water being taken away by the exhaust pipe, as before explained.

The machine is very well made and of large capacity. It is in successful operation at the Brunswick Mill, Carson River, Nevada where six of them are handling the product of 56 stamps, crushing 160 tons of ore a day, and is also in use in other places.

There are possible problems in concentration in California requiring coarse crushing; this has already been discussed, and consequently the accompanying cut of one of the most approved styles of jigs should be of interest.