twenty-four hours with an expenditure of 6 to 8 HP. With the pan amalgamators employed, he has succeeded in reducing the total cost of treatment to 18. 4 d. The cost of treating a ton of ore by the different methods that have been adopted in Transylvania is approximately as follows: Californian stamps : Wooden stamps and pan amalgamators. Ball mill and pan amalgamators Peasant stamps S. d. 60 3 0 2 0 9 2 0 B. H. B. New Mercury-Furnaces. By J. M. MADARIAGA. (Revista Minera, Metalúrgica y de Ingeniería, vol. xl., 1889, p. 305.) The ores of mercury and arsenic, smelted by the El Porvenir Company, Asturias, Spain, were until quite recently treated in intermittent kilns of the Idria type. The ore was piled in lumps, with a small quantity of fuel, on a hollow arch, and the smaller material was moulded into bricks and placed above, whilst a fire lighted on a grate below the arch caused the decomposition of the ore to commence. Several important improvements have recently been introduced by the Company, and at the present time, instead of intermittent furnaces, there are employed a continuous kiln for coarse ore; a channel-furnace similar to those employed at Almadén, and a double-retort furnace for powdered ore. The arrangement of the double-retort furnace is indicated by three drawings (on the scale of 1 to 100) accompanying the original memoir. The chief point of novelty is that the discharging hole is partially open, so as to allow air to enter. This is done without any danger of the fumes escaping by means of the artificial draught produced by a trompe (falling-water ventilator). The retorts are of cast iron, and have a common hearth on which small coal is burnt. Every hour and a half, 110 lbs. of pulverized ore are introduced through the hopper, and in the two retorts 3,527 lbs. of ore are treated in twenty-four hours. When the ore is very rich, it is charged in small lumps, and lime is mixed with it if the proportion of mercury amounts to 15 per cent. For the condensation of the fumes, there are two large chambers, two smaller ones, a wooden compartment with water on the floor, and finally the tromp and the pipe conducting the gases to the chimney, where no trace of mercury can be detected. From the first chambers, 90 per cent. of the outturn is obtained, and from the second nearly all the remainder, for after a year's work not more than 2 lbs. of mercury was obtained from the wooden compartment. During the operation, a considerable quantity of the metal runs out through holes provided near the floor of the condensing-chambers. The loss in this furnace is less than 1 per cent., and the cost of smelting 1 ton of ore is 48. 3d., a sum that might be considerably reduced by employing six, instead of two retorts. In twenty-four hours, the hearth consumes 727 lbs. of small coal, valued at 28. 24d. Thus, with this furnace the results are very satisfactory; and there is the advantage of obviating the necessity for moulding the ore into bricks, an operation that costs nearly 18. per ton. The continuous kiln (illustrated by four drawings on the scale of 1 to 100), is slightly conical in shape. It is 6 feet in diameter above the grate, and 6 feet at the throat, where it is terminated by a spherical dome, in the upper central part of which there is the charging hopper. The kiln may be considered to be divided into two parts, the lower or hearth portion being 9 feet 4 inches in height, and the upper portion, or kiln proper, being 9 feet 10 inches up to the discharge-pipe, and thence to the top of the dome 2 feet 10 inches. The total internal height is thus 22 feet. The hearth forms a chamber smaller in diameter than the rest of the kiln. At 2 feet 10 inches from the ground is the grate, which is 3 feet 7 inches in diameter. The walls continue, with the same diameter, 2 feet 8 inches higher. Above this is a conical segment 1 foot 7 inches in height, the top of which is 2 feet in diameter, and on it is a cylinder 2 feet in height, covered by a spherical dome pierced with holes through which the products of combustion pass from the hearth to the kiln proper. The central aperture is protected by a conical cast-iron cap, in such a way that the gases can escape without allowing ore to fall into the hearth. The hearth-chamber has externally a conical form, and is furnished with an iron cover down which the calcined ore passes to doors at the base. All the internal portion of the kiln is constructed of firebrick, the lining being 1 foot in thickness. A tower, 2 feet in thickness, encloses the whole kiln, and is provided at various heights with apertures through which the progress of the operation may be observed. The discharge-pipe for the fumes is of cast-iron. It is 1 foot 7 inches in diameter, and 13 feet in length, and is placed with an inclination towards the condensing-chambers. On reaching these, it bifurcates so as to communicate separately with the two series. There are two condensing chambers to the right of the pipe, and two to the left. The adjacent chambers communicate by means of two rectangular apertures near the floor, which slopes towards each side of the chamber, and has a current of water flowing under it. These chambers are in communication with four similar smaller chambers placed at a higher level, and from these, four pipes conduct the gases to a large general chamber, whence they are conveyed to a chimney 100 yards distant, by the aid of a trompe, the water of which is also used for cooling the floors of the condensing-chambers. The kiln treats 8.5 tons of ore in twenty-four hours. It is charged every seventy-five minutes with 976 lbs. of ore, and 4.89 lbs. of coke. The grate is only fired in cases of necessity, and when it is required to start the kiln. The calcination is very satisfactorily effected; for the discharged ore does not contain more than 0.02 per cent. of mercury. The condensation is also satisfactory, thermometrical determinations made in March and April, 1889, having given the following results: A test with a gold plate indicated the absence of mercury from the gases in the chimney. The trompe producing the draught consumes 1.1 gallon of water per second, or 15,256 cubic feet per day. The cost of treating 1 ton of coal is :-Labour, 101d.; coke, 1d.; charging and removing ore, 73d.; interest on capital, 71d.; total, 28. 2d. Allowing 28. 3d. for administration, repairs, &c., the cost of smelting 1 ton of ore is 4s. 5d. The following are the results of the first three trials of this kiln : On washing the soot obtained in these three trials, the residue was found to amount to 24,906 2 lbs. This contained 10.87 per cent. of mercury, and yielded 2,707 3 lbs. The accumulations of arsenical residues prevents the campaign lasting longer than in these three trials. The mercurial soot is mixed with coke, and moulded into bricks, which are smelted in the old Idria furnaces with a loss of 10 per cent. of mercury. The loss in the new kiln is calculated to be 8.126 per cent. B. H. B. A Regenerative Annealing-Furnace. By J. vox EHRENWERTH. (Oesterreichische Zeitschrift für Berg- und Hüttenwesen, 1889, p. 477.) At Mr. F. Bosner's wire-works at Augustenthal, near Neuwied on the Rhine, a new form of annealing-furnace with regenerative firing has been successfully adopted for some time past. The furnace has two circular heating-chambers or pits, each taking a single cast-steel annealing-pot, standing upon a rectangular substructure containing the gas- and air-passages and regenerators. The latter are low oblong chambers, measuring about 12 feet in length, 4 feet in breadth, and 2 feet in greatest height. Only two are used in each pair of furnaces, the air alone being heated as the gas is brought hot from the producer. Above the roof of the regenerator is placed a block of fire-brickwork containing the heated air and gas-flues, and the burner, which is a narrow ringshaped passage, terminating at the bottom of the heating-chamber, giving a body of flame that entirely envelopes the annealing-pot placed in the centre. The chamber, which is a little larger than the pot, is about 5 feet high, 4 feet in diameter at the top, a little broader at the bottom, and is covered with a loose iron lid kept gas-tight by sand-joints, having a central passage communicating with the second chamber. In starting the furnace, as soon as one of the chambers is brought up to a strong heat, both receive their charges, consisting of a cast-steel pot, weighing about 18 cwt., and containing 16 to 18 cwt. of hard-drawn wire. The flame, after heating up the first pot passes through the passage at the top through the second chamber and regenerator into the chimney, until the proper heat is attained. The current of air and gas is then reversed, the valve, a single fourway-cock, commanding both passages by a single movement, and the heating of the second chamber commences; the current of spent flame, which at first is notably cooler than the previously heated pot, is passed over the latter until their temperatures are about equalized, when the finished heat is removed, and a new pot is inserted. Three of these double furnaces, taking pots 3 feet in diameter, of the capacity given above, and a smaller one for 20-inch pots, intended for annealing rivets, have been erected in place of an older series of heating furnaces, and the first one has been at work for eighteen months. Each double furnace heats ten pots, or a total weight of 8 to 9 tons of wire in twenty-four hours, so that the heat lasts about five hours. The consumption of coal has been reduced from 12 to 13 per cent. of the weight of the wire heated, which was required in the old furnaces, to from 7 to 9 per cent., giving from 28 to 45 per cent., or an average of 36 per cent. saving in fuel. The wear of the annealing-pots is considerably lessened, their duration having been brought up from 300 to 600 heats, while the labour of handling is considerably lightened owing to the pots being drawn at a lower temperature than was previously the case. The Author gives a design of a similar furnace adapted for reheating steel ingots, and considers that it might be used to advantage in furnaces for cementation and making malleable castings. H. B. Report upon Questions relating to the Employment of Explosives in Presence of Firedamp. (Annales des Mines, vol. xiv., 1888, pp. 197–376.) This is an exhaustive report of a special sub-commission appointed by the French government to determine the behaviour of the different explosives capable of use in mines in the presence of firedamp. The sub-commission was composed of eleven members, of whom Mr. Mallard was president. The report is divided into five chapters, preceded by an historical note, and followed by tables and appended notes. Chapter I. describes the apparatus and mode of experiment. Chapter II. Explosives freely suspended in firedamp mixtures. Chapter III. Explosives exploded in a closed vessel. Chapter IV. Mode of firing shot in the mine; and Chapter V. Conclusions. 1. Even explosives under water can inflame firedamp mixtures with air by means of the dust of the mine. 2. The greater number of known explosives are capable of igniting firedamp mixtures when exploded freely in the atmospheres. Among these explosives are dynamite, gun-cotton (either military or mining, particularly the latter), gelatine dynamite, and Paulille's ammonia dynamite. 3. It is, however, possible to find explosives which detonate at a temperature sufficiently low to avoid inflammation of firedamp mixtures, at least in the great majority of cases, when freely exploded in the atmosphere. Among the explosives experimented on which approximately fulfil this condition are: (1) The intimate mixture of 50 parts dynamite with 50 parts of cystallized carbonate of soda, or sulphate of soda with 10 eqs. water of crystallization, ammonia alum, and ammonium chloride. (2) Moulin-Blanc pyroselin powder. (3) Mixture of 20 parts dynamite, at 75 per 100, and 80 parts of nitrate of ammonia. (4) Mixture of 20 parts of gun-cotton titrating 173 c.c. nitrogen dioxide and 80 parts nitrate of ammonia. (5) Bellite, of which the composition is not known with certainty, and the experiments have not been sufficiently numerous. (6) Favier's explosive containing 90 parts of nitrate of ammonia, 10 parts mononitro-naphthaline, which appears to equal Bellite in security. It requires, however, further experiment. 4. Because of the complexity and variability of the phenomena |