4 Dr. Percy on the Extraction of Gold a7id Silver 



enclosed in 1 30 grs. of assay-lead, and cupelled. The bead not 

 being clean, was recupelled. 1 added 100 grs. of hyposulphite 

 to the filtered solution and boiled, when a dark olive-brown 

 precipitate was thrown down, which was dried, detached 

 from the filter (the same as used in the first filtration) as com- 

 pletely as possible, and heated in a porcelain capsule to expel 

 the free sulphur. A small quantity of black matter remained, 

 which was enclosed in about 80 grs. of assay lead, and cupelled. 

 When the lead was melted, I put the filter on it and inci- 

 nerated, and I also added the bead of silver previously ob- 

 tained, and enclosed in a small piece of assay lead. I ob- 

 tained a good bead of fine silver. However, the cupellation 

 was not perfectly satisfactory, as 1 observed some very minute 

 particles of silver surrounded by black scoria on the sides of 

 the cupel. 



The bead weighed 5* 385 grs. By parting with nitric acid, 

 it yielded of gold O'lOO, or 1-857 per cent. 



6. 1000 grs. of the roasted ore were treated with chlorine 

 precisely in the manner described in experiment 5, and left 

 during four months. Bubbles of gas continued to be evolved 

 sensibly for a long time ; and even at the end of the four 

 months, on stirring the ore, still continued to be disengaged 

 from its surface. The clear supernatant solution was de- 

 canted, and the residue treated with a cold solution of 200 grs. 

 of hyposulphite of soda; it was left for two or three days, fil- 

 tered and washed with cold water. I then digested the fil- 

 trate on the sand-bath with excess of sulphuric acid until the 

 odour of sulphurous acid ceased to be detected. I washed 

 the precipitate with boiling water, when after long washing, 

 it still continued to become turbid by the addition of BaCi 

 (from PbCl). The dry precipitate was seen to be mixed with 

 shining, colourless, acicular crystals. 1 roasted till no odour 

 of sulphurous acid was evolved, and then cupelled the residue 

 with 200 grs. of lead. There was evidently a considerable 

 quantity ol matter present which would not pass into the cupel. 

 1 recupelled the bead with a small additional quantity of lead. 



I obtained a bead of fine silver, weighing 5'80grs. On the 

 addition of carbonate of potash to the decanted supernatant 

 liquor, a copious white precipitate was thrown down. 



7. I digested 1000 grs. of the finely-pounded roasted ore with 

 a solution of hyposulphite of soda containing 200 grs. of the 

 salt, at a temperature just warm to the hand, and then filtered. 

 I boiled the filtrate, which became brown. 1 added to the 

 boiling solution excess of dilute sulphuric acid, and continued 

 to digest for some time at about 212° F., stirring continually. 

 I filtered and dried. 1 detached the precipitate from the fil- 



