Français : Four à griller les minerais d'argent ou d'or, de Carl August Stetefeldt (ou Charles A. Stetefeldt).

Français : Roasting kiln by Carl August Stetefeldt (also Charles A. Stetefeldt), design to roast gold and silver ores.

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Stetefeldt's Roasting Furnace.

This furnace, now being built at Austin, Nevada, is represented in Fig. 9, showing a vertical cross section. The furnace at Reno, Nevada, has a dust-chamber in place of the flue, b, of Fig. 9, the omission of

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which simplifies the construction without injury to the good results of roasting. The furnace has three important departments. 1st. The roasting shaft, a, twenty-five feet high and five feet wide at the bottom, narrowing somewhat toward the top, to prevent the adherence of dust to the wall. It is a simple shaft of common bricks, built as smooth as possible. On the top of the shaft, at a', is placed an iron feeder, through which a permanent and uniform feeding of the pulverized ore, already mixed with salt, is effected. The ore falls on the bottom, e, and when half a ton or a ton is accumulated, it is drawn out through the door, f. 2d. The fire-places. There are three gas generators, constructed similarly to that of the copper-refining furnace at Mansfield, Prussia. The cover is taken off and the charcoal introduced. The cover is placed again on its frame, which contains sand in a groove in order to shut off the draft entirely. The slide door near g is drawn out, and the charcoal falls on the grate, h, through which as much air is admitted as is necessary. There are also two canals on each side of the grate, one of which is shown by dotted lines, i, both communicating at k. Through these canals is regulated the admission of the air for oxidizing or burning the carbonic acid, created above the grate, h. In the flue, d, air and gas meet together, and the burning product heats the furnace. Two of these generators heat the shaft, a ; the mouth of one is shown in the drawing by c, the other is on the opposite side, and therefore not visible in the plan. The two generators are constructed exactly like g, with the exception that the flue, d, is not inclined, but horizontal. The flue, d, as well as the generators above the grates, are lined with fire-bricks. 3d. The dust-chambers. With the draft, the gases from the shaft, with a part of the fine ore dust, pass through the vertical flue, b, then through the horizontal one, m, into a series of chambers, ?i, of different sizes. The first four chambers, n, are smaller than the four following, which are not represented in the diagram ; from the last chamber the gases draw into the chimney. The dust can be removed from the bottom of the chambers through

the doors, o, o. Almost all the dust is regained, and not in a raw condition, as from dust-chambers of reverberatory furnaces, requiring re-roasting, but perfectly chloridized, which is principally due to the auxiliary generator, g y and the longer contact with the chlorine gases.