removed, and the section drawn back till the clutch coupling disengages, when the shaft can be lifted out of the box. 4. The Boss settler, which is used in the Boss continuous process, is shown in Fig. 1. This settler differs from those previously described mainly in the shape and arrangement of the stirrer and shoes. The pan is 8 feet in diameter, with a cast-iron bottom and wrought-iron sides. The bottom of the pan is flat, and the central cone has a much wider base than is usual in the ordinary forms. There is a slight trough in the bottom, next to the sides of the pan. The shoes are of iron and are much larger than those used in the ordinary settler, each shoe extending across the bottom from the base of the cone to the edge of the outside groove, at a slight inclination from the radial line instead of radially. They are bolted to a muller ring or plate, which is in turn bolted to the three legs of the driver. The shoes do not touch the bottom of the pan, but work quite close to it. The angle at which the shoes are set induces a strong current on the bottom and keeps the pulp from packing. The driving and following gears are proportioned so that the stirrer makes about 20 revolutions a minute. (The speed of the amalgamator mullers is about 60 revolutions.) As a rule, no additional settling apparatus is used in Bossprocess mills. 5. The chemical mixer, which is frequently used in the treatment of somewhat refractory ores, is of the same size as the settler and nearly identical in construction. It has, however, wooden sides, as they withstand the reaction of the chemicals much better than wrought iron; and a steam cone is run up inside the main-bottom cone, the heat from it greatly assisting the action of the chemicals. chemicals are relatively light and the motion of the stirrer slow, so that the solution, is strongest in the top of the charge, where the pulp meets it on entering the mixer; and the discharge is practically from the bottom, a vane or wing just in advance of the discharge pipe deflecting the The pulp into it as it rises from the bottom at the outside of the pan. In this way, the chemicals are retained longer in the pan and the necessary chemical action on the ore is completed sooner. The number of mixers used in the series depends on the character of the ore and the capacity of the mill. The more refractory the ore, the longer must it be exposed to the action of chemicals; consequently, very refractory ores sometimes have to be passed through several mixers in order to give the chemicals sufficient time to act on them. The chemicals are fed into the mixers by an automatic chemical feeder. When mixers are not required, the chemicals (salt and bluestone) necessary for amalgamation are fed into the first pan by one of these feeders, which is placed between the first two pans of the series, and if any additional chemicals are necessary, they are fed in by another feeder farther down the line, usually between the last two pans. 6. The mercury system is entirely mechanical. The mercury is stored in an iron reservoir and is run into the pans through pipes having inverted siphon traps, where they connect with the pans to exclude the pulp. The amount being charged into each pan is regulated by a cock in the pipe near the pan. The total amount of mercury used is shown on the dial over the reservoir. The shaft which carries the hand on the dial has a small sprocket on it, over which passes a link-belt chain, one end of which is fastened to a cast-iron float on the mercury in the reservoir, while the other end carries a counterweight which keeps the chain taut. As the mercury falls in the reservoir, the float sinks with it and draws the hand around on the dial. The mercury bowls of the pans and the first settler are connected by pipes with a receiving tank, into which the amalgam may be run by merely withdrawing the plugs in the bottoms of the bowls. The amalgam can be drawn at will from the receiving tank into canvas straining bags, from which the excess mercury drains off. The strained mercury runs through pipes into the boot of a small link-belt elevator, by which it is raised and dumped back into the storage reservoir, to be used again. 7. In the Boss process, when the ore is crushed wet, the pulp runs directly from the stamps into the grinding pans. The proportion of water ordinarily used in wet crushing in stamp mills would render the pulp altogether too thin for amalgamation; so the size of the screen meshes is increased considerably and the water cut down to the proper proportion for pan pulp. In this way the same crushing capacity and the average size of the product is practically maintained, while the pulp can pass to the grinding pans without intermediate settling. When the ore is very refractory and has to be crushed dry and roasted, the roasted ore is mixed with water and fed continuously into the grinding pans by a screw feeder. Ordinarily the roasted ore is spread out on cooling floors to cool before going to the pans, but in the more modern continuous-process mills there is no handling of the ore from. the beginning to the end of the process. The ore passes from the bins into revolving drying furnaces; from the driers it goes directly into the automatic feeders of the stamp battery; the pulp from the battery is elevated by a continuous-belt elevator into the hopper of the roasting furnaces which are generally of the revolving type (HowellWhite continuous or Brückner cylinder)-where the salt is added to chloridize the ore; after passing through the furnace it goes to the mixing pan, from which the screw conveyer carries it to the grinders; and from here on the operation is as previously described. In old-style mills the roasted ore is spread out on a cooling floor and cooled, and is then carried to the mixer by hand. 8. Clean-Up Pans.-Clean-up pans are small amalgamating pans, used in gold and silver amalgamating mills for cleaning dirty or impure amalgam before retorting, and for working up small quantities of heavy blanket concentrates, battery sands, etc. They are made in various sizes, from N. M. III.-17 15 inches to 5 feet in diameter, 4-foot pans being the most commonly used in large mills. The construction and mechanism are the same as those of ordinary amalgamating pans For cleaning amalgam, wooden muller shoes are generally used, as they are required more for stirring than for grinding. The dirty amalgam is charged into the pan with enough additional mercury to make it perfectly fluid and it is then thoroughly stirred. The foreign matter rises to the top of the liquid bath of amalgam and is washed away by water running through the pan. For treating concentrates and battery sands, iron shoes are used, as it is necessary to grind the pulp, and iron shoes not only wear better but clean the surface of the gold, so that it amalgamates more readily. When the pans are used for both purposes, the deep wooden shoes are shod with cast iron. The wooden blocks extend above the surface of the amalgam, so that no amalgam will be deposited on top of the shoes when the pan is drained. In many small mills, amalgam is still cleaned by hand, grinding with more mercury in iron pots or hand mortars, and concentrates and battery sands are panned with an ordinary miner's gold pan, to recover free gold and amalgam. All modern mills, however, are fitted with some form of mechanical clean-up apparatus-usually pans. A cleanup pan known as the Berdan pan is considerably used in Australia and New Zealand. It is merely a revolving pan, slightly inclined from the horizontal, and containing an iron ball, which naturally stays at the lower edge as the pan revolves, grinding the ore as it is carried around by the pan. 9. Clean-Up Barrel.-The clean-up barrel is made and operated in the same way as the amalgamating barrel shown in Fig. 2, but is unlined, and not so large-being usually 3 feet in diameter and 4 feet long. The amalgam and mercury are charged into the barrel; the barrel is then nearly filled with water, closed, and revolved for several hours at about 20 revolutions a minute. Scrap iron is sometimes added, but this flours the mercury and does not materially assist the operation, and its use is now being generally abandoned. At the end of the agitating period the barrel is opened and washed out with water-the tailings being run over amalgamated plates or through some other form of amalgam saver-while the amalgam in the barrel is removed, strained, and retorted. 10. Barrel Amalgamation.-The Freiburg, or barrel, process of amalgamation is not much used in America. A few attempts at barrel amalgamation have been made, but in most cases they have given way to the pan process, which is somewhat quicker, and by most metallurgists considered superior to the barrel process. However, a description of the barrel and a brief outline of the process will be given. 11. The Barrel.-The amalgamating barrel is cylindrical in shape, usually about 4 or 5 feet long inside and the same in diameter. Fig. 2 shows one form of barrel. Some barrels have a replaceable lining of wooden blocks, about 5 inches square and 3 or 4 inches thick, set on end, as shown in the illustration; this lining can be replaced when it wears out, and the barrel will last indefinitely. The barrel is made of soft pine staves, 2 or 3 inches thick, bound together with iron bands; and the joints between the planks forming the heads are grooved and fitted with tongues of hard wood. When the barrel is not lined, the staves are |