1847.1 On the Refinage of under standard Silver. 565 



This converts the metallic copper into oxide of copper. When cool 

 the mass is boiled, 100 lbs. at a time, in a leaden boiler, for about an 

 hour, with 401fes of sulphuric acid and 200 lbs of water. Most of the 

 copper is thus recovered in the state of sulphate of copper solution, 

 which is poured off into tanks to crystallize. What is undissolved by 

 the acid is tile- dried, and a small portion, about ten tola weight, of the 

 residue melted for trial. If the trial ingot is malleable and soft the 

 whole mass may now be melted into ingots to close the account. For 

 although these ingots will be much worse than standard, they are free 

 from lead and devoid of brittleness, and consequently fit for alligation. 

 On the other hand if the trial ingot be brittle the mass should be again 

 roasted and treated with sulphuric acid as before. And according to 

 the original quality of the silver this may need three such operations. 



In refining 100,000 Rs. value of such understandard coin, about 

 90,000 Rs. value will be returned at once refined above standard — 5000 

 will be found in granules — 4000 to 5000 will be recovered by roasting 

 and by sulphuric acid, and from 500 to 1,000 will remain as chloride 

 of silver and very finely divided metallic silver, which is slowly depo- 

 sited from the sulphate of copper liquid, as a white slime or mud, con- 

 sisting of the chlorides of silver, copper and lead, sulphate of lead and 

 metallic silver. This mud is tile-dried and treated as follows : — 



100 parts by weight are well mixed with 50 of dried carbonate of 

 soda, and 20 of powdered charcoal, the mixture melted in black lead 

 pots and poured into conical moulds — on cooling a mass of lead 

 containing all the silver is found at the point of each cone. This lead 

 usually contains 20 to 25 per 100 of silver, and the precious metal is 

 extracted by cupellation. The quantity of argentiferous lead to be 

 cupelled from the refinage of 100,000 tolas of silver will range from 

 2000 to 4000 tola weight. If black lead pots are not available this 

 part of the operation may be conducted successfully in the native 

 cylinder furnace above described, merely substituting cow-dung for the 

 charcoal, and mixing the mass into balls. 



By careful attention to the above description no failure or difficulty 

 need be dreaded in large silver refinages. The advantages of the process 

 may be briefly summed up — rapidity, economy, salubrity and safety of 

 the bullion. Before this method was introduced in the Calcutta mint 

 the refinage of silver to the value of a lac of rupees was the work 



