Manual of Assaying Gold, Silver, Copper, and Lead Ores

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1889 Excerpt: ...the largest roasting dish which will go in the muffle; but above those weights use the frying-pan, or else roast several charges in the dishes, and unite them for fusion. Place the roasting dish, with contents, in the forward part of the muffle, before the latter has reached a dull red heat. The ore is to be continually stirred with a stout wire, having a loop at the end at right angles to the wire, A. In a little while, minute sparks will be thrown off, and the ore will begin to glow in places like burning charcoal. Stirring should be continued till the glowing ceases (by which time there will be little danger of fusion), and the whole seems of one color, and yielding to the stirrer like dry sand. The dish can now be moved back to the hottest part of the muffle, and left unstirred for some little time. When, on bringing out to the open air and stirring, the ore gives off neither fumes nor odor, the operation is finished, the ore being now sweet. Let cool, and examine. The roasted ore should be of a dull, dead; earthy color (usually some shade of red or black), having no metallic lustre, containing no large, hard lumps, and having no portions adhering to the dish. See that all the charcoal is burnt out. Should the ore contain many lumps, grind in a mortar, mix with charcoal, return to the dish, and repeat the roasting. If the assayer is too busy to spare the time needed for stirring, let him take the dish, and spread its contents out thinly, or ridge the ore from the center to the edges, so as to increase the surface exposed, and place it in the muffle, and warm it gently for a time; then increase the heat for about the same length of time; finally heat quite hot. Take out dish, cool, grind finely, return to dish, and roast again. Repeat the roa...