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 1-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.

Dry concentration is not discussed in this article, because it is little used in California, and in fact is rarely adopted if water can be obtained in sufficient quantity for wet concentration, because the latter gives uniformly better results with less cost, and less wear and tear.

In conclusion, I will state that these notes have been written hurriedly, as but little time was given me in which to prepare them. I have attempted, however, to be fair and just in my statements and criticisms.

CHLORINATION.

(By WM. IRELAN, Jr., State Mineralogist.)

This method of extracting gold from the auriferous sulphurets is recognized in the metallurgical circles of the old world as the Plattner process, and is so called in honor of the inventor. The honor of its introduction and successful adaptation to the working of our sulphuretted residues is due to the well known mining engineer and metallurgist Mr. G. F. Deetken, by whom it was first brought into this country.

Owing to the expense of manipulation, cost of material, and other obstacles, Mr. Deetken had much to contend with, but his well known skill and scientific ability enabled him to reach a successful issue and to become a metallurgical benefactor.

Since the demonstration of its successful workings on our concentrated sulphurets, a general knowledge of the manner of its application has been distributed by means of our scientific and other papers; also, books have been written by two of our well known metallurgists, in which the whole process is explicitly dealt with.

The first of the above mentioned works on the subject was issued by the late G. Kustel, in the year 1868, new edition 1880; and the latest exhaustive description is from the pen of Charles Howard Aaron, in 1881. Both authors were at the time of writing practically engaged in working the sulphurets of the State by this method.

The subject is inexhaustible, and of vital interest to the mining industry of our gold-bearing sections.

This article is not intended to give the detailed manipulations of the process, as the works above cited were written especially as working descriptions, and can be purchased of any of the booksellers.

THE ROAST.

This is the most important of any part of the process, and upon its completeness depends the success of the operation; therefore, too much care cannot be exercised in this branch of the operation.

In roasting, the point to be attained is the complete oxidation of the baser metals whose soluble salts would become precipitants for gold in the leaching vat. If the concentrated sulphurets have become lumpy, it will be necessary to recrush them, that the roast may secure complete oxidation.

It frequently happens that too much material is put into the furnace at one time: Mr. Aaron advises, for the reverbratory, from ten to twelve pounds for every square foot of hearth as the correct charge. The furnace should be fired up several hours before being charged with the dry sulphurets, and the heat should be of a degree just sufficient to ignite the sulphur after the material has been evenly spread over the hearth. Too great a heat will matte the easily fusible sulphides, thereby necessitating a withdrawal of the charge from the furnace and a repulverization. The presence of galena requires a low temperature and continual stirring. Mr. Deetkin discovered that the presence of lime and magnesia, owing to their