64 



METALLURGY. 



lead and copper, a small quantity of iron pyrites ; if 

 they do not, some of this is usually mixed with them, 

 by which the extraction of the silver is facilitated. The 

 ore, after being freed as much as possible from its 

 stony ingredients, is mixed with common salt, in the 

 proportion of 8 or 9 per cent, if the ore contain 8 oz. 

 per quintal ; and 10 or 12 per cent, if more silver be 

 contained in it. It is then exposed for some hours on 

 the floor of a reverberatory, till the vapour cease to 

 come off; the mixture being frequently stirred to ex- 

 pose the whole of it to the flame. If, when removed, 

 too little or too much of the salt have been added, 

 (which the workman by experience easily knows, ) the 

 proportions must be adjusted, by adding either more 

 of the salt or of the ore, and the mixture is again roast- 

 ed in the reverberatory. During this part of the ope- 

 ration, the sulphur of the ore is partly dissipated in the 

 form of sulphurous acid, part of it in the state of acid 

 combines with the alkali of the salt, and the muriatic 

 acid set free unites with the silver. When the matter 

 is cold, it is reduced to powder in a mill, and then 

 amalgamated with about an equal quantity of mercury. 

 The amalgamation is performed in barrels, which are 

 made to revolve, or in tubs which contain an appara- 

 tus for keeping the mixture in constant agitation. The 

 mixture is put into these vessels, and made into a 

 thickish paste with water, and kept agitated for about 

 two days, and after the amalgama has fallen to the 

 bottom, it is withdrawn through an aperture in the 

 lower part of the vessel. What remains is washed, by 

 which more of the amalgam is got from it, and the re- 

 sidual matter, if the ore contained a great deal of silver, 

 is again roasted with about 3 per cent, of sulphur, and 

 subjected to a similar process, by which the whole of 

 the metal is extracted. The amalgam procured by 

 these different operations, is freed of its superfluous 

 mercury, and is then subjected to distillation, by which 

 the whole of the mercury is expelled and the silver is 

 left ; retaining, however, a little copper, which is re- 

 moved by cupellation. 



Fusion. The ore generally subjected to the process 

 of fusion, is lead glance, which almost always contains a 

 small quantity of silver. When lead mines are wrought 

 on account not only of the lead, but also of the silver, 

 the earthy matter mixed with the ore is considerable, 

 and the quantity of silver is very various in different 

 mines. In some, as those formerly wrought in York- 

 shire, the silver amounted to about 230 oz. in the ton, 

 while the Durham and Westmoreland mines afford on- 

 ly 17 oz. per ton. 



The first part of the process for procuring silver 

 from these ores, consists in stamping and washing as 

 has been already described, after which the substance 

 contains silver, lead, iron pyrites, blende, and earthy 

 matter. The ore is then roasted in a reverberatory to 

 drive off the sulphur, taking care that the heat be not 

 so high as to fuse it, and that when it begins to adhere 

 together on the surface, it be well stirred. In about 

 five or six hours, the flame from the ore changes from 

 blue to white, charcoal in powder is then thrown in, by 

 which part of the lead ore is reduced, and collects at 

 the bottom ; when a -sufficient quantity is formed, 

 quicksilver is mixed with the scoria to thicken it, and 

 the fused metal is drawn off. After this, the heat is 

 continued, and the metal as it is formed, is repeatedly 

 taken out, the temperature being increased towards 

 the end of the process, to cause the scoria to become 

 more liquid, so as to allow the metal to fall through 

 it. The metal as it is collected, is covered with char- 



coal ; and the scoria which is formed, is removed. It 

 is then covered with saw-dust, pieces of wood, and 

 a little resin, and constantly stirred; and when the 

 flame ceases, it is poured into moulds. The scoria 

 procured in the different operations, is afterwards 

 heated in a blast furnace, to procure the lead from it. 



The lead containing the silver obtained by the above 

 operations, is then subjected to the process of refining, 

 which is the same as cupellation, only performed on a 

 large scale. For this purpose, a reverberatory furnace 

 is employed, but the process differs in different places, 

 owing to a difference in the nature of the ore. In 

 England, the cupel or vessel in which the refining is 

 performed, is composed of 6 parts of bone ashes, and 1 

 of fern ashes, made into a paste with water. In the 

 centre of this there is a shallow cavity, for the recep- 

 tion of the metal, and at one end there is a hole for the 

 escape of the litharge, formed during the operation ; 

 the litharge flowing into this, along a groove made in 

 the cupel. When the cupel is heated, the metal is put 

 in through an aperture in the furnace, and a stream of 

 air is made to play on it, by which the litharge is formed, 

 and escapes along the groove. As this groove is de- 

 stroyed, the litharge is made to run along another, and 

 in this way the whole of it is withdrawn. The metal 

 in the cupel is again subjected to a similar operation, 

 after which it is poured into moulds, and formed into 

 ingots. 



In other places, the lower part of the reverberatory 

 is covered with wood ashes and clay, so as to form a 

 cupel. On one side of the furnace, there is a hole for 

 the exit of the litharge; and on the opposite side is 

 another for the admission of air to the surface of the 

 metal, which is introduced through an aperture above, 

 to which a cover is adapted. After the lead is melted 

 and brought to a red heat, the blast of air is admitted, 

 and the scoria as it collects is removed. When the 

 litharge is formed, the heat is increased, and the quan- 

 tity becomes greater, and is withdrawn through the 

 opening in the furnace. At the same time some 

 lead is volatilized. Towards the end of the pro- 

 cess, the litharge which comes off, contains a small 

 quantity of silver, and is therefore kept separate from 

 the rest. After the whole of the litharge is removed, 

 and the surface of the metal in the furnace becomes 

 bright, a quantity of water is poured on it, to prevent 

 the metal from spirting, which it is apt to do when 

 congealing. The metal thus obtained, is subjected to 

 a similar operation for about five hours, in a smaller 

 furnace, and at a higher temperature, by which it is 

 freed from the lead. 



Silver is also occasionally procured from the silver 

 ores by the process of fusion. The process, as carried 

 on in France, consists in mixing the ore (which con. 

 tains native silver, sulphuret of silver, iron pyrites, ar- 

 senic and cobalt,) with lime, the scoria of a former 

 operation, and slag from an iron furnace to make it 

 more fusible. Galena and litharge of a previous pro- 

 cess are also added. These, when mixed, are exposed 

 to heat in a blast furnace, along with charcoal, by 

 which a metallic matter, composed of silver and lead 

 is obtained. This is again fused with litharge, and 

 the metal procured, is afterwards subjected to the pro- 

 cess of cupellation, at a temperature higher than that in 

 the other instances, owing perhaps to the presence of 

 iron, which occasions a considerable loss of silver. 



When the ore also contains copper, a different pro 

 oess is followed for procuring silver from it. The ore 

 is mixed with another ore, containing silver, iron, and 



Metallur- 

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