This metal occurs In many minerals, but not in such quantity as to make its extraction profitable. It is almost exclusively obtained from cobalt speiss at the Saxon smelt-works, the residue containing about 7 Per cent. of it. The operation of smelting bismuth is extremely simple : the metal, having bat weak affinity for other substances, is obtained by heating its ore in a liquation furnace in a cast-iron retort set on an incline, at the highest part of which the crude ore is charged; at the lowest angle is placed a cast-iron bowl, into which the metal flows. The furnace is illustrated in Fig. 7. large as marbles, is charged into each retort a, of which there are usually 4 in a furnace side by side; this quantity nearly fills a retort, so that the upper part is empty. The lower end is closed with a clay slab ft, provided with an aperture for the discharge of the melted metal. The pipes, when properly ignited, soon cause the metal to flow into the dishes c, which contain some charcoal-dust, and are heated by a separate fire d.
By applying a brisk fire /, and stirring the ore, all the metal contained in it is obtained within 1/2 hour, the residue is scraped out of the retort Into a trough « with water, and the pipes are filled afresh, About a ton of ore is melted in a day of 8 hours. The metal is re-melted, and cast into iron moulds in the form of ingots. The metal thus obtained may be purified by re-melting in a flat bone-ash dish, at a low heat, removing the dross as it appears on the surface. It is advisable to melt the metal thus reduced to a purer form, in a graphite pot, and then cast it into the mould for ingots. Bismuth cannot be freed from silver by these means, in consequence of which the commercial article always contains some of that metal.
The bismuth ores at Joachimsthal, Hungary, are smelted in crucibles with J their weight of scrap-iron to combine with the sulphur, 1/2 soda carbonate to convert the silica into a soda silicate slag, and 1/2 each of lime and fluor-spar; 1 cwt. of the mixture is put into each crucible, part of the soda carbonate being used to cover the charge. The crucibles are closed by lids, and strongly heated till the contents become pasty, when they are well stirred, and, after complete fusion, ladled out into conical iron moulds, wherein the bismuth collects at the bottom.
Commercial bismuth is largely contaminated with arsenic, iron, and silver; these do not interfere with its general application in alloys, but much of the arsenic can be removed by heating under charcoal in crucibles, and the silver, when sufficiently abundant, can be re-coverel by cupellation at the cost of the bismuth being converted into oxide. Metallic bismuth is remarkable for its brittleness (somewhat less than antimony), low melting-point, great tendency to crystallize, property of expanding during solidification (increasing 1/32), and diminishing in specific gravity under strong pressure.