matter. Ores of the most various characters have been roasted with equal success. Even ore containing nothing but silver-bearing galena was treated without any difficulty. In this respect the furnace is admirably adapted to roast ores with large amounts of antimonial and leadbearing minerals.

Amount of salt.-In reverberatory furnaces ten per cent. of salt is generally used. This amount may be safely reduced to six per cent. for very rich ores, and to three and four per cent. for low grade ores, in the Stetefeldt furnace. No experiments have as yet been made to determine if this percentage can be reduced still more. The difference in the percentage necessary is explained by the fact that in the Stetefeldt furnace all the salt is decomposed and utilized, while in the reverberatory furnace a large percentage remains in lumps and entirely unchanged.

Fuel.-The amount of fuel necessary to heat the shaft depends very much upon the character of the ore. The more sulphurets an ore contains the less fuel is required to roast it. The furnace in Reno uses

on an average about two cords in twenty-four hours. With this amount between 12 and 15 tons of ore are roasted daily, which is as much as the battery crushes. But the same fuel would just as well roast 20 tons of mainly sulphuret ores, which increase the heat in the shaft when introduced in larger quantities. How many bushels of charcoal a furnace with gas generators would require we are not able to estimate reliably at present; but for most localities in Nevada charcoal will be as cheap if not cheaper than wood.

Labor.-At the mill in Reno eight men are employed to run the furnace. Of these three are firemen, three discharge and cool the roasted ore, and two watch the feeding and elevating machinery. If gas generation with charcoal is used, the labor of three men can be saved, and the two men who watch the feeding machinery can very well charge the generator shafts. In this way only five men will be required to run the furnace. Taking these facts in consideration, it is easy to estimate how much the Stetefeldt furnace cheapens the expense of roasting. In a mill of 20 tons capacity, in twenty-four hours, at least ten reverberatory furnaces would be required. The labor needed in twenty-four hours is, 2 carmen, 2 pulp-coolers, 2 oremen, 30 roasters; total, 36 men; fuel, at least 10 cords of wood in twenty-four hours; salt, 10 per cent. or 4,000 pounds. In the Stetefeldt furnace these 20 tons are roasted with 8 men, (or 5 men if charcoal is used as fuel,) 2 cords of wood, and 2,000 pounds of salt; saving by use of Stetefeldt furnace, every twenty-four hours, 28 men, (now, and 31 men with charcoal furnaces,) 8 cords of wood, 2,000 pounds of salt. Besides this, the original cost of the Stetefeldt furnace is less than that of a corresponding number in capacity of reverberatory furnaces. It requires less repairing and does better work. I may mention, furthermore, an experiment made in Reno to try the capacity of the furnace. One ton of pulp was accumulated and put through the furnace in thirty minutes, indicating the furnace to have a capacity of 48 tons in twenty-four hours. Ninety-one per cent. of the roasted ore was found to be chloridized.

*

CHAPTER LXXXIX.

ELECTRICITY APPLIED TO METALLURGY.

The following article from the San Francisco Mining and Scientific Press of May 22, 1869, gives an account of various so-called electric, or electro-magnetic processes for the reduction of ores. On the practicability of such methods I must decline to express an opinion. As I have already hinted in speaking of the supposed effects of electricity in ore deposits, there is no particular distinction between electrical reactions, in which a metal is reduced, at the cost of a chemical decomposition and so-called ordinary chemical precipitates. The precipitation of copper from solution by means of metallic iron and its galvanic deposition in electroplating, are both according to chemical equivalents. Indeed, electrical decompositions have given the foundation for the modern system of chemical equivalents. A good many so-called galvanic or electric metallurgical effects, such as the reactions of sodium amalgam, of magistral in the patio, and of vitriol and salt in the pan amalgamation, might as well be called chemical. The use of the more obscure name only misleads the practical operator, who, believing in some mysterious catalytic influence, does not employ sufficient quantities of his reagents, and obtains, in consequence, imperfect results, The convertibility of chemical activity into galvanic currents does not, it seems to me, offer any theoretical gain in economy. The consumption of chemicals is still necessary. But the case is different when magneto-electric machines are used. These promise at least a conversion of mechanical force into chemical activity, and the question whether this conversion would be practically profitable is well worthy of consideration. Mechanical force can be gained in so many ways, and applied to so many other purposes, that its auxiliary use in this respect might become, under some circumstances, a great economy. I am not very sanguine as to its present application; but the idea deserves mention, if only as a new and ingenious deduction from the modern theory of the correlations of force. The following is the article referred to:

"The working of ores of silver and other metals by the aid of electricity was probably first proposed by Professor Bequerel, who devoted a number of years to experimenting on the subject, without attaining, however, any really practical results, so far as concerned economy. According to his plan the ores were first subjected to roasting, in order to convert the metals to be extracted-which were mostly in the state of sulphurets-into chlorides and sulphates. These products were then dissolved, the former in a solution of chloride of sodium, and the latter in water, whereupon the liquids thus obtained were respectively placed in vessels containing plates of copper, tinned iron, or prepared carbon, which served as negative electrodes, and porous cups filled with a solution of chloride of sodium, and containing the positive metal, consisting of pieces of either zinc, iron, or lead were introduced to complete the voltaic combination. To establish the electric circuit the negative elec trode of one apparatus was then, by means of a wire or otherwise, brought in metallic contact with the positive electrode of the other, &c., and upon the last connection being made the reduction of the metals held in solution ensued. This process, which was especially intended for the beneficiating of silver ore, was finally abandoned because the percentage of metal obtained from the ore was far less than that yielded

* Part III, Chap. LXII of this report.

by the Freiberg process of amalgamation, with which it also compared unfavorably regarding expense.

"This whole subject assumed a new phase when, about ten years ago, the first attempts were made in this country to apply the electric current directly to the ore without previous roasting. These attempts were probably suggested by the property possessed by metallic sulphurets of conducting electricity. If in a solution of chloride of sodium sulphurets of silver are brought in contact with the positive electrode of a galvanic battery, they are decomposed, chloride of silver is formed and dissolved, and from it metallic silver is thrown down upon the negative electrode. This process is materially aided by the presence of chloride of copper, produced either by the mutual decomposition of sulphate of copper and chloride of sodium, or by the electrolytic action between a solution of chloride of sodium and a positive electrode of copper.

"It seems Mr. John Scott, of San Francisco, was the first who undertook a series of trials to test the practicability of subjecting silver ores, plunged in a solution of chloride of sodium and salts of copper, to the action of voltaic electricity. Others, more or less conscious of the object and the scientific principles involved, stepped from time to time in his wake, failed, and returned to their legitimate callings, until several months ago public attention was anew, and in a higher degree than ever before, drawn to the subject by an exhibition of experiments on an extensive scale by Messrs. A. L. Nolf and F. L. A. Pioche. Their process, as publicly shown, is substantially as follows: They immerse the ore, finely pulverized, in a solution of chloride of sodium and sulphate of copper contained in a wooden vat, the inner sides of which are, to within six or eight inches from the bottom, lined with sheet copper. In the center of the vat is an upright shaft, to which arms or stirrers are attached, which are also covered with sheet copper, and extend downward far enough to be in contact with a layer of quicksilver resting on the bottom. This quicksilver, and through it the arms or stirrers, are connected with the negative pole of a powerful galvanic battery, while the copper lining of the vat is connected with the positive pole. To allow the introduction of steam, the vat is provided with a well-fitting cover. During the operation the shaft is revolved by power derived from a small steam-engine, and thus the ore pulp is kept in agitation, so that the particles of sulphurets contained therein may successively be thrown in contact with the positive electrode, in order to become decomposed. "Now it must be borne in mind that in the application of electricity to the treatment of ores containing sulphurets, and such other metalliferous minerals as must be decomposed before their constituent elements can combine to salts capable of forming electrolytes, from which metals may be reduced, it is a necessary condition for the success of the operation that each particle of such minerals be not only brought in contact with the positive electrode, but also kept in contact with the same until it is decomposed.

"This condition, it is evident, cannot be complied with by a mere agitation of the ore pulp between electrodes placed vertically, or otherwise so arranged that a contact between each particle of sulphuret and the positive pole-plate is in great measure but a matter of chance, and generally of but momentary duration; unless the operation be continued for an indefinite length of time-or, indeed, the chemical ingredients added to the ore pulp be of such kind and quantity that the intended result would almost as well be reached without the application of electricity.

"An invention by Dr. A. F. W. Partz, of Oakland, for which a United

States patent has lately been granted, is intended to meet the require ment above referred to, and thereby render practicable a new metallur gical process which may yet be destined to play a conspicuous part in our mining industry. The apparatus which he employs may be briefly described as follows:

"A cylindrical wooden vessel, about 6 feet long and 4 feet in diameter, a segment of which, amounting to nearly one-third of its periphery, is missing, is horizontally so suspended on two gudgeons fastened to its sides in the line of its axis that the opening left by the missing segment is on top. This opening is provided with lids which are closed during the operation. Lengthwise through one of the gudgeons is bored a hole, just wide enough to allow a steam pipe, which in the vessel is bent downward, to pass through it and remain in place when the gudgeon is turned. The bearings in which the gudgeons rest are supported by pieces of timber, between which thick plates of glass are inserted, to prevent loss of electricity by "leakage." The inner periphery of the vessel is, up to the height of its axis, lined with a sheet of copper, which forms the positive electrode, and is, by means of wire which passes through the side of the vessel, brought in metallic connection with one of the gudgeons. Eight or ten inches from the periphery, below the axis of the vessel and parallel with the same, a number of tubes of brass or copper about two inches in diameter are placed in a segmental row a few inches from each other, resting at one end of the vessel upon a wooden, and at the other upon a metallic support. These tubes constitute the negative electrode, and are, by means of a wire attached to the metallic support, and which passes through the side of the vessel, brought in metallic connection with the other gudgeon. Upon either gudgeon rests the end of a flat spring, and to these springs the respective poles-wire of a galvanic battery, or some other generator of dynamic electricity, are fastened.

"Having thus given an outline of the principal features of the apparatus, we will proceed to give a brief description of the manner in which argentiferous ores are worked by its means.

"The cylindrical vessel is, to about one-third of its capacity, filled with a solution of chloride of sodium, to which pulverized ore is added until the mass forms an easily-flowing pulp. By power applied to a crank fastened vertically upon one of the gudgeons, the vessel is put in a slow swinging motion, the crank alternately deflecting from 40 to 50 degrees either way from its vertical position. This motion is intended to prevent the earthy portion of the ore from settling, and at the same time to facilitate the sinking of all heavier particles, (sulphurets, &c.,) and their concentration upon the positive pole-plate, where they collect in a layer, which is kept agitated just enough to insure the constant forming of new points of contact with the pole-plate. The electric connection being made as above stated, and steam being turned on, a vigorous electrolytic action ensues. Water and chloride of sodium are decomposed, oxygen and chlorine are disengaged at the positive electrode, and ready to enter into the new combinations they effect, under the influence of the electro-current, the decomposition of the sulphurets and other metalliferous compounds resting upon the positive pole-plate, while they also attack the plate itself, forming with the material thereof oxychloride of copper, which in turn aids in the formation of chloride of silver. The latter dissolves in the solution of chloride of sodium present, and from it metallic silver is reduced and deposited upon the tubes constituting the negative electrode. As the silver thus reduced is apt to be in a loose, flocculent, or spongy state, the tubes must be amalgamated with mercury to better insure its adhesion and collection,

and the amalgamation must from time to time be renewed, which may be accomplished by merely dropping some mercury into the vessel; because on coming in contact with the positive pole-plate the mercury is dissolved, whereupon it is reduced again to its metallic state, and deposited together with the silver. The form of tubes was chosen for the negative electrode on account of the large surface which they afford, and the facility with which they are removed and stripped of the adhering amalgam. If, under circumstances, it should, however, be deemed preferable to employ a layer of quicksilver in their stead, the same may be placed in a flat vessel, the negative pole-wire dipped into it, and the vessel suspended in the liquid. An addition of sulphate of copper to the ore pulp quickens the operation, but is not essential for its success. The positive pole-plate being dissolved in proportion nearly equivalent to the silver reduced (i. e. about 32,108) must, from time to time, be restored. To this end the remaining portion of the plate need not be removed, it being necessary only to cover the spots where the metal has disappeared with patches of copper fastened to the vessel with copper nails. "The above-described apparatus is also to be employed for the extraction of gold from auriferous pyrites; but if so employed, a positive electrode of iron or carbon (slabs of Bunsen coke or of graphite) is substituted for that of copper. The same change becomes necessary in the treatment of sulphurets and other ores of copper, in which also solid rods of copper in place of tubes are used as negative electrodes. According to the character of the ores, an alkaline sulphate or nitrate, or sulphate of iron, may sometimes advantageously be substituted for chlo ride of sodium, or used in connection therewith.

For reasons of economy, the employment of galvanic batteries is admissible only in the working of ores of silver; for other ores, magnetoelectric machines must be used in their stead, so that, in generating the electric forces required, carbon may be consumed in place of zinc."

APPENDIX.

PRODUCTION OF QUICKSILVER.

The production of quicksilver during the year 1869, was as follow:

* Returns for months not given. Product for the year estimated. Grand total: 33,713 flasks, at 76 pounds, or 2,579,044 pounds.

This being a very small production compared with the ordinary demand, the price of quicksilver has in consequence somewhat advanced.