where the gold, on account of its weight, sunk and was amalgamated. After passing the amalgamator, the material ran over a simple riffle sluice, and any escaping amalgam was caught in the riffles. The skimmings from the wells of the amalgamator and the tailings from the blankets were passed through a rubber, where they were ground between iron surfaces, cleaning the gold and freeing it from gangue; as soon as it was cleaned it was amalgamated on copper plates in the rubber. The rubber was merely a flat box with a false bottom of alternate strips of wood and cast iron, extending across the box from side to side; above this was a muller, shod with plates of cast iron similar to the bottom plates, bolted to level blocks; narrow, amalgamated copper strips were fastened on the sides of the blocks. The muller was hung from four swinging rods, so that the shoes barely cleared the bottom, and was given a short backward and forward motion by a connecting-rod and an eccentric on a shaft at the lower end of the box. The stroke of the muller was about 4 inches and the faces of the shoes and dies were 4 inches wide. 38. Besides the foregoing machines, there are numerous patented amalgamators used occasionally here and there, none of which, however, gives any promise of driving amalgamated plates and pans out of the market, although some are founded on theoretically correct principles. A great many of these make the galvanic or electric current an essential feature, the idea being that galvanic or electrolytic actions keep the mercury clean and lively-which is perfectly true; but mechanical drawbacks prevent the general adoption of these machines. To this type belong the Molloy hydrogen amalgamator and the Bazin centrifugal amalgamator. HUNTINGTON MILL 39. It is not probable that the Huntington mill will ever generally displace the stamp battery, though it may to a considerable extent. When it is desired to amalgamate as much gold as possible inside the Huntington mill, the water-supply should be kept down low, but not so as to clog the screens. The pulp then remains in the mill longer before discharging and the gold is given more time to amalgamate. As in the stamp mill, a decrease in the water-supply is attended with a corresponding decrease in the capacity of the mill. On the aprons, a moderately thin pulp, flowing readily, is best; too thick a pulp will clog the plates with sand. ACCESSORY APPARATUS 40. Amalgam Strainers and Safes.-In silver pan amalgamation mills, where large quantities of amalgam are handled, the liquid amalgam is poured into an amalgam safe similar to the one illustrated in Fig. 3. The top and bottom of the safe are made of cast iron and the body of wrought iron. The top is concave, with a hole in the middle through which the amalgam drops into the conical canvas bag or strainer beneath. The hole is protected by a raised cap, cast on the cover or bolted to it, to prevent the theft of amalgam. The excess of mercury in the amalgam is strained through the canvas by its own weight and falls into the bottom of the safe, leaving the lumps of nearly dry amalgam in the bags. The strained mercury is drawn off into flasks or reservoirs, or, in the continuous-system mills, is raised by a quicksilver pump or elevator to the receiving reservoir. The cover is hinged, and can be lifted to obtain access to the strainer. FIG. 3 The strainer is fastened to a ring, and can be taken out and cleaned. A door in the side gives access to the bottom of Both this door and the safe without removing the strainer. the cover are kept locked. 41. Retorts.-Mercury is separated from the gold in the amalgam by distillation. In small silver or gold mills, FIG. 4 where the amount of amalgam handled is comparatively small, cast-iron retorts of the type shown in Fig. 4 are generally used; but in larger silver mills, where a large quantity of amalgam is produced, retorts of the type shown in Fig. 5 are necessary. The small pot retort, Fig. 4, does not require a special fireplace, although one is generally provided, but may be heated in a crucible furnace or blacksmith's forge. A special furnace is, however, always provided for large retorts. A melting furnace, in which the bullion is melted to be cast into bricks or bars, is frequently FIG. 5 built in connection with the retorting furnace, as shown in Fig. 5. The retort, 12" in diameter, is usually placed immediately above the grate, but where large quantities of amalgam are retorted, if the furnace is left unattended for any time, a retort which is set immediately above the fire is apt to become overheated, and the weight of the metal inside then causes it to sag, ruining it completely. To prevent this, the retort is sometimes arranged with the fire at one side and a fire-bridge between, the retort being supported at several points. In most modern retorting furnaces, a number of small rectangular openings, connecting the fire-chamber with the flue at intervals along the top of the arch, causes the heating to be distributed evenly along the length of the retort; and the draft can be very delicately regulated and the heat localized, if desired, by the use of individual dampers over these holes. Many furnaces are still built, however, with only a single flue connection at the front end. 42. Charging the Retort.-Before charging the retort with amalgam, the inside surface is chalked or coated with a thin wash of clay or is lined with a few thicknesses of paper, the ashes of which effectually prevent the gold from adhering to the sides of the retort. In large stationary retorts, the amalgam is placed in iron trays which slip into the retort and save much trouble in charging and handling. The lumps of amalgam from the strainers are broken up, placed in the retort or in trays, and pressed down firmly. In many mills the amalgam is packed with the head of a bolt, but most millmen disapprove of this practice, as packed amalgam requires longer to retort and is apt to hold some unvolatilized mercury in the center of the lumps. The condenser pipe should be carefully cleared of all obstructions, and if the amalgam is put directly into the retort, it should be spread evenly and in such manner that by no mischance can this pipe become clogged, as an explosion would be apt to result, filling the retorting room with poisonous mercury fumes and greatly endangering the health and lives of the |