Annual report of the State Mineralogist for the year ending ... . ERALOGIST. one, and was formerly used exclusively. It is based on the rapidoxidizability of lead when heated with free access of air and on thenon-oxidizability of silver under the same circumstances. The apparatus used for this operation differs. The German Cupelling Furnace Has a solid refining bed and a movable cover, the English a movablebed and a solid cover. The former is the older one. A description andillustration of it is given by Agricola in his book on metallurgy, printedthree hundred years ago. It is constructed of s
Annual report of the State Mineralogist for the year ending ... . ERALOGIST. one, and was formerly used exclusively. It is based on the rapidoxidizability of lead when heated with free access of air and on thenon-oxidizability of silver under the same circumstances. The apparatus used for this operation differs. The German Cupelling Furnace Has a solid refining bed and a movable cover, the English a movablebed and a solid cover. The former is the older one. A description andillustration of it is given by Agricola in his book on metallurgy, printedthree hundred years ago. It is constructed of stone or brick and refract-ory material. The refining bed has an oval form, and is made of acourse of firebricks set on edge, on which are spread several layers ofmarl. The cover is a shallow iron dome plastered on the interior sidewith fire clay. It may be removed by means of a crane and fireplace is lateral, and connects with the furnace proper by meansof a wide opening, B. Lead is charged during the operation through theopening marked D in Fig. K£3J. F, F are apertures for the admission of two tuyeres. The blast which;is directed on the surface of the lead bath assists in the oxidation and idrives the scum and litharge towards the aperture E, through which itflows out on the floor. This opening is almost completely closed upwith fire clay at the beginning of the operation, during the progress of:which it is gradually cut down to suit the level of the litharge. The refining bed of marl is concave, the center being about twelveinches deeper than the rim. After the bed has become thoroughly driedthree fourths of the bullion to be treated, which is cast in small hemi-spheres, is piled on it, the convex surfaces downward so as not to injurethe lining. An average charge weighs about one hundred hundred-weight, so that seventy-five hundredweight are placed in the cupellingfurnace at the beginning, and twenty-five hundredweight at a laterperiod of the operation. Upon
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