by air-pressure. Electric overhead travelling-cranes command the whole of the floor, and may be brought into operation in connection with any tank at will. Electric tramways of 20 in. gauge are brought on to the working floor of each hall, and other similar tramways run beneath the tanks. Fig. 101A shows a general view of one of the electrolytic tank rooms at the Anaconda works. In practice, the blister copper, containing generally about 98 per cent. of copper, together with arsenic, antimony, iron, lead, tellurium, selenium, and about 110 oz. of silver and oz. of gold per ton, is cast into the form of anodes. The anodes are conveyed in the electric tramway to the depositing rooms; here they are arranged in a frame and conveyed by the electric crane to the vat for which they are intended. Meanwhile, this tank will have been cut out of the electric circuit, and out of the flow of the liquid, both the current and the circulation being continued without interruption through the remaining tanks); the cathodes, with their charge of electrolyte copper and the remnants of the anodes, will have been lifted out by the crane and carried to the tramway; and the slimes, or "silver mud," will have been washed out into leadlined cars beneath the tanks, to be transported to the silver refinery. The vats are then refilled with solution; the crane brings up first the frame of anodes, which are lowered into the exact position required, and then a similar frame of cathodes, which are treated in the same way; and finally the tank is included in the electric circuit. The whole operation of discharging and re-charging one tank should occupy scarcely more than one hour. The system of checking the progress of the work is especially worthy of mention. Each series of five tanks is connected up to a kind of dynamo commutator, in such a way that the opposite poles of the same series of five vats are joined up to radial copper plates at the opposite ends of one diameter of the commutator. These plates are all insulated from one another. A yoke-piece with two brushes, diametrically opposite, is revolved around the commutator once an hour; and the brushes are connected to an automatically-registering voltmeter, so that each series of 5 vats is individually connected up to the latter instrument, and the slope of potential between the terminals of each of these series is therefore registered serially once every hour. The manager is thus able to detect and to locate precisely any irregularities that may be taking place. There are 120 men employed in the works, including the foreman, assayers, and clerks. In the depositing houses there are 75 men, of whom 50 are engaged in the older building, whilst only 25 are required for the same outturn of copper, in the new building, owing to the perfection of the labour-saving appliances used. The average wage is $3 per man per diem, and the cost of fuel is $5.50 per ton; but the latter will shortly be reduced to $2 per ton. About 100 tons of copper are at present being treated per diem, half in each building; and the cost of refining, including that of treating the silver mud by chemical processes, amounts to $14 (£2, 18s.) per ton of refined metal. Neither the current density employed, nor the E.M.F. required for each pair of electrodes is given; all that is stated on this subject is that in Thofehrn's refineries the current density generally used is 10 to 20 amperes per sq. ft. The copper produced is melted into ingots or wire bars at the cost of about $4 per ton; and this metal, in the form of hard drawn wire, containing, as it must at least, a trace of cuprous oxide, is found to have an electrical conductivity of 98 (Matthiessen's standard), and a tensile strength of 64,000 to 65,000 lbs. per sq. in.; the number of twists obtainable in 6 in. of No. 12 wire is 80; elongation, 1 per cent.-TRANSLATOR]. Thofehrn's New Process.-The same number of the Engineering and Mining Journal (loc. cit.) describes a new process in which the copper is deposited upon a long hollow cylindrical cathode 8 ft. long and 3 ft. in diameter, which is immersed in the electrolyte, and is revolved at a low speed, whilst the copper is deposited upon it with a current density of 50 to 100 amperes per sq. ft. During the time of depositing, numerous jets of the electrolyte solution are caused to play under pressure upon the surface of the cylinder.* It is stated that the crystals of copper are deposited in the form of microscopic octagonal hair-like filaments, which become felted and compressed by the jets of liquid; and that the cylinders of copper when they have been deposited an inch thick and have been detached from the cathode cylinders may be rolled direct. It is said that the wires are over 15 per cent. stronger than those prepared by the old electrolytic refining process followed by fusion; and that the expense of such an electric refining of the metal to produce * [A similar device has been adopted by Graham (English patent 986, Jan. 14, 1896. According to his specification, a nearly saturated solution of copper sulphate, containing 5 ozs. of strong sulphuric acid per cb. ft. of water is used as electrolyte, and is stored in reservoirs placed at a height of from 1 to 2 ft. above the electrolytic tanks, thence it is conveyed to -in. jets that deliver it in a stream upon the surface of the cathodes, which are placed at a distance of 1 in. from the orifices of the jets. It is stated that a current of 300 amperes per sq. ft. may be employed with safety at all points within the sphere of influence of the jets; beyond this area, it is obvious that the deposit would be pulverulent and useless. The radius of the protected area is found to be 5 ins., and the number and disposition of jets employed must be arranged accordingly. The anode should have a surface area eight or nine times greater than that of the cathode, and its shape should preferably be that of a corrugated spiral or of a grid, through which the electrolyte streams are directed upon the cathodes. The edges of the latter are protected by an insulating material.-TRANSLATOR.] the bars required for the rolling or wire-drawing mill is $16 (£3, 6s.) per ton. One distinct advantage in the use of these jets is obviously to be found in the certainty that the electrolyte at the surface of the cathode is constantly and thoroughly renewed, so that a very much greater current density may be employed than would otherwise be possible. No details whatever are given concerning the process, and it is therefore premature to criticise it. It may be noted that the same paper states that white metal anodes with 75 to 80 per cent. of copper have been employed in this process with success, but no hint is given as to the manner in which difficulties that have baffled the attempts of previous inventors have been obviated.-TRANSLATOR.] Modified System of Deposition.-It need hardly be pointed out that many other modifications of the plant originally described have been made, and have received titles, suggestive of the credit due to those who made the new 66 discovery," or "improvement." Reference to the names of the original inventors is usually omitted. The Stalmann Process.-The original voltaic battery has been made the foundation of another system of arranging electrodes, which has come into use in various modifications, and in some cases with the stated object of economising cathode plates. Schnabel* describes one of these methods (in which, however, special separate cathode plates are used), and states that he has seen it in use in the Anaconda Works at Montana, U.S.A. Without this testimony it would have been very difficult to believe that this most inconvenient arrangement should have found any favour in practical work; but as it has been shown to be possible, it will be necessary to describe the apparatus and the method shortly at this point, the account being taken from the patent specifications of Stalmann† whose process it is. Stalmann couples the electrodes of each individual bath in series, suspending an anode first, and then cathodes and anodes alternately, united in pairs, until at last a cathode plate ends the whole series. The first anode and the last cathode are connected immediately with the main leads of the circuit, or are joined up in series with other baths similarly arranged. The details of the electrode connections in the bath are shown in Figs. 102 to 105. In arranging the first pair of electrodes, either the cathode plate, k, is fastened directly to the anode, a (Fig. 102), or each anode plate, a, is connected with a cathode plate, k, by means of a wire or by the short copper bars, v, lying on the rim of the vat (Fig. 103), or, finally, the anode, a, is united to the cathode, k, in the manner shown in Fig. 104, with * C. Schnabel, Handbuch der Metallhüttenkünde, vol. i., p. 270 (1894). + U.S. A. Patents 467,350 and 467,848, Jan. 19, 1892. a plate, i, of insulating material separating them, so that only one side of each plate comes in contact with the solution. The lastnamed method is the latest. The pairs of electrodes are suspended in the baths after the fashion adopted in the older systems. If the electrodes are not attached by screws to supporting arms as shown in Fig. 103, the anode plates, a, are cast with projecting lugs, x (Fig. 105), by which they are supported on the rim of the bath. The electrolyte vats (H and H1) are double, one being placed within the other, whilst the intervening space is filled up with paraffin wax, tar, or other similar material; they are made of wood, and the inner vessel is provided internally with a series of wooden studs, F, on its side walls to prevent any displacement of the electrodes. The connections of the electrodes and conductors will be understood on reference to Fig. 106, in which a is the first anode, k the last cathode, and ak the intermediate double electrodes. It is not easy to understand from this patent specification what advantages Stalmann's arrangement possesses over the other systems in use. Fig. 107.-Scheme of electrical connections in Hayden's vat. The Hayden, Smith, and Randolf Processes.-Hayden* simplifies this apparatus by omitting all the cathode plates except the one connected to the negative wire of the generator. He joins up the first anode plate to the positive lead from the dynamo, and suspends behind it a series of crude copper plates insulated from it, and from one another, and finally connects a plate of pure copper to the negative lead. The pure copper is therefore deposited on those sides of the intermediate plates that are turned towards the first anode, whilst the metal is at the same time dissolved from the other sides, which face towards the last negative plate. But, unfortunately, the crude copper plates, which are always of cast copper, are never quite uniform in structure; or, even if the electrodes could be obtained perfectly homogeneous, certain irregularities, due to the clinging of the insoluble residue to the surface and the like, would be unavoidable; there must, therefore, be a more rapid solution of the metal at some places than at others. Cavities are thus formed, which, in course of time, extend to the pure metal deposited (by this time to some thickness) on the other surface; and it goes without saying that the pure copper must then be dissolved. Fig. 107 shows the electrical connections in the Hayden bath in which a is the anode, and k the cathode plate. The intermediate plates, z, serve as cathodes on their left-hand, and anodes on their right-h and surfaces. [The Hayden process, which was introduced in 1886, may perhaps Engineering and Mining Journal (New York), 1892, vol. liv., p. 126. |