TELLURIUM ORE. 139 



From the solution the gold is precipitated by a con- 

 centrated solution of sulphate of protoxide of iron. 

 When the metal has subsided, it is washed and ignited. 



The liquor filtered off from it is considerably con- 

 centrated by evaporation in a flask, allowed to cool, 

 and mixed with a solution of an alkaline sulphite, 

 when the tellurium is precipitated as a gray powder. 

 After standing for twelve or twenty-four hours it is 

 filtered off, and washed, first with dilute sulphurous 

 acid, and then with water. The solution must be 

 made strongly acid in every case, to insure the com- 

 plete precipitation of the tellurium. 



Gold and tellurium may also be precipitated together 

 by an alkaline sulphite, and the latter metal then ex- 

 tracted by means of nitric acid. The filtered liquid is 

 again evaporated to a small bulk, and mixed with an 

 alkaline sulphite, when, in most cases, a farther quan- 

 tity of tellurium is obtained. 



II. The ore, freed from most of the gangue by 

 means of hydrochloric acid, is intimately mixed with 

 twice its weight of bisulphate of potassa ; 4 to 6 times 

 its quantity of bisulphate of potassa is then fused in a 

 capacious Hessian crucible at a gentle heat, and into 

 the fusing salt the above-mentioned mixture is intro- 

 duced by small portions at a time, waiting between 

 each addition, until the frothing of the mass has sub- 

 sided. When this has ceased, and a sample of the 

 mass being taken out appears quite white, the fused 

 mass is poured off from the gold, which has settled at 

 the bottom of the crucible. The remainder of the salt 

 is then washed out of the crucible with hot water con- 

 taining sulphuric acid, and the gold collected. 



The mass which was poured off is then dissolved in 

 this water, with a farther addition of sulphuric acid, 

 the solution filtered off from the sulphate of lead, &c., 

 and then the silver precipitated by means of hydro- 

 chloric acid. 



