6 Dr. Percy on the Extraction of Gold and Silver 



viously observed under the same circumstances, again occurred 

 on the surface. I treated with a solution of 200 grs. of hypo- 

 sulphite of soda. On testing the wash-water with HS water, 

 S was precipitated, and there was not the slightest dark dis- 

 coloration. I proceeded exactly as before, and cupelled with 

 about 60 grs. of assay lead. The bead of fine silver weighed 

 0*675 gr. I again treated the residual ore in a similar manner 

 with CI for about an hour and a half, and then digested for a 

 considerable time on the sand-bath. On the following day I 

 dissolved out with a solution of 200 grs. of hyposulphite. I 

 treated the filtrate as usual with dihite SO-^, and tested the 

 wash-water with HS water. I proceeded as before. I em- 

 ployed 100 grs. of assay lead for cupellation. The bead of 

 fine silver weighed 0*154. The total amount of fine silver 

 obtained is 6*636 grs. By parting with NO^ I obtained of 

 gold 0-197. The silver therefore contained of gold 2*968 

 per cent. 



I now boiled the residual ore with a solution containing 100 

 grs. of KCy, filtered and washed. By addition of HCl in 

 excess to the filtrate, a white precipitate was produced ; but 

 on continuing the digestion until the odour of hydrocyanic 

 acid could no longer be detected, it became dark-coloured, 

 which I believed to be owing to the presence of S in some 

 form. I digested the precipitate with NO\ and obtained a 

 pale blue solution, which did not become in the slightest de- 

 gree turbid by the addition of HCl. On the filter remained 

 only a minute quantity of matter, like sulphur in appearance, 

 gomewhat discoloured ; and by heat the characteristic odour 

 of sulphur was evolved, and only a minute quantity of matter 

 was left. 



8. In another experiment, in which I heated 1000 grs. of 

 thej^nf/y-pounded ore, triturated after roasting, with a solu- 

 tion of 200 grs. of hyposulphite, I obtained a bead of fine 

 silver weighing only 0*81. 



9. I digested 1000 grs. of roasted ore with a solution of 

 common chloride of lime (hypochlorite) on the sand-bath 

 during two or three days. 1 then washed and digested the 

 .residuum, at a 'warm temperature, with a solution of 150 grs. 

 of hyposulphite of soda. I filtered and washed. To the fil- 

 trate I added an excess of dilute SO^ and heated till the su- 

 pernatant liquor became quite clear. I filtered, washed 

 slightly and dried. I enclosed the filter, with its contents, in 

 .200 grs. of assay lead, and I subsequently added on the cupel 

 100 grs. I obtained a bead of fine silver weighing 5*469, and 

 containing gold, but only to the extent of -02. I do not, 

 Jiowever, place much confidence in this determination of the 



