64 MINERALOGY. 
To obtain lead from its sulphuret, the latter is roasted in the open air, by 
which a great part of the sulphur is burned. The remainder, consisting of 
partially desulphuretted lead and sulphate of iron, is melted with charcoal 
and limestone. The lead thus obtained still contains the other metals which 
were originally mixed with it. It is called workable lead when in this state, 
and is, first of all, to be treated for silver. For this purpose it is brought 
into a cupellation furnace, so constructed, that a constant stream of air 
may pass over the melted metal. By this means the oxygen of the 
atmosphere coming in contact with it, converts it into oxyde of lead, which 
exhales to a considerable extent, but is principally drawn and let out 
through an adjoining aperture. The silver does not combine with the 
oxygen during this operation, and while the oxyde of lead or litharge is 
constantly being removed, the silver remains behind, until finally every 
particle of oxyde of lead has disappeared. The silver then undergoes a 
further preparation after being removed. The oxyde of lead is either sold 
in this form, as litharge, or it is melted afresh with charcoal, and reduced 
again to the metallic state. | 
Lead, on account of its malleability and readiness of fusion, its ease of 
working, and its great abundance, is one of the most important of all metals. 
Its oxydes and salts are also of extensive application. Litharge is used in 
glazing pottery and in the manufacture of glass; an addition of minium or 
red oxyde of lead, to melted glass, renders it transparent, and constitutes 
what is known as flint-glass, in contradistinction to crown-glass, into whose 
‘composition little or no lead enters. The glass used in porcelain painting, 
as also the pastes of the artificial gems, all contain a necessary proportion 
of oxyde of lead. Of the salts of lead, white lead is the most important. 
This is a carbonate of lead, or a carbonate combined with a hydrated 
oxyde. Acetate of lead, or sugar of lead, is used in dyeing, and in the 
preparation of many mineral colors. 
2. Vitreous Silver, or Silver Glance. 
This is a simple sulphuret of silver, and consists of 87.032 per cent. of 
silver and 12.968 of sulphur. It crystallizes in many-faced crystals of the 
regular system (pl. 33, figs. 30, 33, 35, 36, 45), and also occurs in reticulated, 
arborescent, filiform, and amorphous masses, as also in plates. It readily 
melts before the blowpipe, emits the odor of sulphurous acid gas, and leaves 
behind a button of silver. It occurs in veins, accompanying other ores of 
silver, and is not abundant except in Saxony, Bohemia, the Tyrol, Hungary, 
Spain, and Mexico. It is very remarkable in being a malleable ore, 
flattening out under the stamper. 
In places where sulphuret of silver, native silver, and other rich silver 
ores occur, the metal is obtained by amalgamation. This consists in 
reducing the ore containing silver into a very finely divided condition, and 
in this state shaking it up with mercury; the mercury combines with the 
silver, forming an amalgam. Should sulphuret of silver be in question, it 
will be necessary first to drive off the sulphur by roasting the pounded ore 
with salt. During this operation the silver is converted into chloride of 
silver and metallic silver, which mixture is to be treated with water and 
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