420 



SMELTING PROCESSES 



Gold Separation Process. 



If the silver is very poor in gold, two or three dissolvings of six centners refined blick-silver each, are conducted in 

 the same kettle, so that the gold of eighteen centners or so is concentrated in it. The gold residue so left is very 

 full of impurities — silver vitriol, metallic silver and anhydrous salts of copper and iron — and for its further 

 purification, is boiled for three hours with concentrated acid, and allowed to cool and settle, the clear liquor being 

 transferred to the silver precipitation vessel. It still contains anhydrous sulphate of copper and iron and metallic 

 silver. It is boiled with hot water in a wooden tank lined with sheet-lead, in order to dissolve the salts. This boiling 

 is repealed three or four times. The wash water of the boiling is precipitated with copper by itself, because a great 

 deal of sulphate of silver is dissolved in it. It is colored green from the iron vitriol. The thus desilverized liquid 

 is used to sprinkle roasted ore. The rest of the wash water of this gold is used like the wash water from the 

 precipitated silver, to dilute the concentrated solution of sulphate of silver. The gold residue is now twice again 

 well digested with 200 pounds of concentrated sulphuric acid in an iron kettle, the first time for eight hours, and the 

 second time for onohour. This is done for the perfect separation of the undissolved silver. From forty centners of this 

 material, enough auriferous residue is obtained to fill two small kettles. This is then put into a porcelain crucible, 

 and boiled with hot water, in order to get rid of the sulphate of silver. The wash water is continually tested for 

 silver. 



The gold residue now, for the first time, assumes the brownish yellow color of finely divided gold. It is well 

 dried on plates of graphite, and then twice heated to redness, after being mixed with sulphate of soda, and boiled 

 with fresh acid After each boiling, it is boiled with water. It is now melted in a Hessian crucible with saltpetre, 

 to get out any lead that may still remain in it. After cooling, the crucible is broken, and the gold is melted ovor 

 again in a graphite crucible, in order to free it from the saltpetre slag. It is then poured out, 99.4 per cent, fine, 

 bito small cast-iron moulds, in which form it is sold. A pound of gold is worth. 400 rcichsthaler. 



Bismuth Separation Process. 



It, has been stated that bismuth exhibits a stronger affinity for silver than does the lead, and it is to this cause 

 that we are to ascribe the marked predominance of bismuth over other metals in the hearth of the refining furnace, 

 This hearth saturated with the last impurities which leave the silver as fused oxides, contains 20 p.c. of silver. It 

 is treated for bismuth as follows: The hearth is stamped fine and digested in the cold, in earthen ware vessels, with 

 equal parts of hydrochloric acid and water, in which the bismuth dissolves, while lead and silver remain in the residue 

 The bismuth solution is drawn oil' by means of leaden syphons, and the residue is washed several times thoroughly, the 

 wash-water being poured with the first solution into a large reservoir in which there is sufficient water. The whole, 

 of the bismuth is precipitated, as basic terchloride of bismuth, in the form of a white mud. This is then filtered off 

 and dried, after which it is molted in an iron crucible with the addition of calcined soda, coke-dust, and glass-powder, 

 and reduced to metalic bismuth. 



VlTmor.izATioN. This process consists in boiling the completely oxidized concentration matt with 

 dilute sulphuric acid, by which treatment the copper is dissolved, and the silver and sulphates of the other 

 metals remain as residue. This solutionis allowed to stand and clarify itself, and then crystals are obtained by its 

 concentration. These crystals (so called raw crystals) are dissolved and the solution concentrated again, giving crys- 

 tals of sulphate of copper SO pure as to be lit to bring into commerce. 



The concentration matt is first stamped and sifted in order to get the grains as nearly as possible of one size. It 

 is then roasted in the Hearth and Muffle Furnaces, but the muffles are not used in roasting it. The matt is put into 

 the furnace by means of iron boxes. The weight of a charge is 10-12 centners and the length of time of roasting Lfl hours. 

 The roasting is begun with a light lire until the matt, by reason of its percentage of sulphur, ignites. During the 

 last 4 to 8 hours it requires a strong fire for the purpose of decomposing the metalic oxides. The charge is turned every 

 two hours (from the chimney to the lire bridge). Besides this it must bo well worked over with the shovel and the 

 lumps which are Conned, broken up. In front of every working door is a workman who has an eight hour shift. In 

 24 hours the consumption of fuel is 7 bushels of coal. The concentration matt melts so easily that in spite of the 



