C.—s

52

(Fig. 4), for the purpose of causing the solution to circulate when the drum is revolving, and also for removing into one or both standards any slime that has gathered in the shaft. The screw may be the same length as the shaft, or it may be only such length as may be desired to accomplish the object for which it is intended. Both tanks are connected with each other by a pipe, in, to enable the solution to circulate freely. The anode, as indicated by b (Figs. 2 and 3), consists of a number of carbons arranged in the drum in one or more rows. Carbons are used for the reason that metals would be immediately attacked and dissolved by the chlorine. The current is conveyed to the carbons by means of brushes, n, or by rollers. The brushes or rollers bear upon the metal rods or band, c, and are fastened in brackets, o, to standards, g, care being taken to properly insulate them, and they are connected at p with one pole of the source of electricity by wire, q, while the other pole is connected with the shaft or standards themselves at r, so that both shaft and standards form the negative pole in the machine. Upon the drum being set in motion and the current switched on, the current is conveyed by wire, q, to the brushes, in, bearing upon the band, c, to the carbons, b, forming the anode ; then through the electrolyte to the shaft, d, and the standards, g, and back to the battery or source of electricity. The electrolyte is common salt water, such as sea-water. The drum is charged with the ore through the opening, s, which is provided with means of tight shutting, a rubber ring being inserted to prevent leakage. The metals in the pulverised ore are constantly thrown against the anodes when the drum is revolving, and these form frequently part of the anode itself, and thereby are brought into most intimate contact with the nascent chlorine and oxygen generated at the positive pole, and are readily dissolved. The metals in solution are deposited electrolytically in the shaft —this being the negative pole—as a black slime, and are then conveyed into the tanks by the archimedean screw, where they can then be easily collected and smelted. " The shaft may be made stationary, and the drum caused to revolve thereon, but it is preferable to cause the shaft also to revolve, to insure the delivery of the slimes into the tank. Several of these machines may be placed in the circuit. The passing of the shaft through the interior of the drum may be dispensed with in the manner shown in l?igs. 5, 6, and 7. In these figures ais the drum containing the carbons, as before described, and having a large opening, t, on each side (Kg. 6). This opening may be of any convenient size, and the larger it is the less the resistance will be. This opening is entirely covered with asbestos-cloth, and to each side of the drum is fastened the flange of shaft, d, d —which is made well- or funnel-shaped, as shown—by means of screws, or in any other suitable manner, care being taken to prevent leakage of current and solution; and this shaft passes, as before, through stuffing-boxes, /, in tanks, g. Upon the drum being charged and set in motion, the current, as in the former case, enters the drum through the carbons, and leaves it again through the bell-shaped shaft-ends, the asbestos dividing the two polos. The chloride of gold is deposited in the shaft and in the tanks, all of which form the negative pole. Hydrogen is generated from the decomposition of the water at the negative pole ; and to allow this to escape, and further to prevent polarisation, and also to allow any slimes which may accumulate to be withdrawn, openings, provided with valves, w, are arranged in the bell, which, on reaching a certain point, are opened automatically to allow the escape of hydrogen, and on passing a given point again they are automatically closed. Instead of the bell-shaped ends terminating through the stuffingboxes in the standard-tanks, the drum may be provided on each side with a large iron cap, serving as a cathode, asbestos being fastened between the iron and the drum to separate the carbons from the iron, which latter forms the negative pole. The drum may then rest upon wheels, and suitable gearing provided by which it can be revolved. Of course, proper means must be applied to allow the hydrogen to escape." Only a small working model is yet exhibited, and there may be many small points that will have to be considered when a machine is constructed to work upon a large scale ; but as far as I have examined this machine it appears to be well suited for the extraction of gold from the ores. Annexed are plans showing the principle of the machine, which will make the foregoing description more clearly understood. TREATMENT OF SILVER-ORES. Seeing that there is a very large percentage of silver in some of the quartz lodes in the North Island, especially in the Marototo, Whangamata, Waihi, and Karangahake Districts, and that no proper process has yet been adopted for the treatment of the ores, it may be interesting to those who are engaged in this class of mining to give a description of one of the successful processes adopted in mining districts in America. The following is an extract from a paper read before the American Institute of Mining Engineers, by 0. A. Stetefeldt, and published in their transactions in 1886, which process seems to be applicable to some of the ores found in the Marototo and Karangahake districts. ■ ' "Russell's Process for the Lixiviation of Silver-ores. " All silver-ores that do not carry a large percentage of lead or copper can be treated by Russell's process with success and economy. It is not meant that from all ores containing considerable quantities of lead and copper a high percentage of silver can be extracted by this process. Such ores, however, will, in many localities, be reduced to better advantage by smelting. In case lead-bearing ores are suitable for concentration, it may be profitable to concentrate them by Krom's dry system, obtaining a smelting product high in lead, and to lixiviate the tailings and the dust. This plan has been adopted in a mill recently erected in Oortez District, Nevada. " The dry system of concentration deserves the preference, because it delivers the tailings and the dust in a condition ready for chloridizing-roasting. In wet concentration the drying of the tailings would be expensive, and there would be a considerable loss of silver in the sluice.