2 Dr. Percy on the Extraction of Gold and Silver 



the dry way, and then proceeded with experiments on the 

 extraction of those metals by the wet way, the results of which 

 I now communicate. 



The mean of two assays of the roasted ore by the dry way 

 gave of fine silver containing gold — 

 7*977 grs. in 1000. 

 55*839 in the pound avoirdupois. 

 260f oz. in the ton. 



The silver contained of gold per cent. 3*78. 



Therefore, the total quantity of fine silver in 1000 grs. of 

 roasted ore is 7*676, and of fine gold 0*301. 



Or, 250| oz. fine silver in the ton, and 9 oz. 16 dwts. fine 

 gold. 



1. Ammonia extracted some silver from the roasted ore, 

 notwithstanding the roasting towards the last was effected at 

 a bright red heat. 



2. A solution of hyposulphite of soda also extracted from 

 it a very sensible quantity of silver. 



3. 1 digested 1000 grs. of roasted ore for a few hours with 

 a dilute solution of hyposulphite of soda, containing 150 grs. 

 of the crystallized salt. The digestion was made at a tem- 

 perature just warm to the hand. I filtered, washed well, 

 added to the filtrate an excess of dilute sulphuric acid, and 

 then boiled. Almost immediately after the addition of the sul- 

 phuricacid, sulphurous acid was evolved and sulphur deposited; 

 but until the solution became hot, it did not acquire a dark 

 colour. I boiled for some time, stirring constantly until the 

 supernatant liquor became bright and the dark precipitate 

 subsided. I filtered, washed well and dried. I. enclosed this 

 precipitate in a sheet of assay-lead*, and cupelled. I obtained 

 a bead of fine silver weighing 4-*800. An accident occurred 

 in this experiment, which may have caused a slight loss. I 

 treated the bead with nitric acid, and obtained a sensible 

 residue of gold. I parted, with the usual precautions, and 

 melted the residue of gold before the blowpipe. The bead of 

 fine gold weighed 0009. The silver therefore contained 0*187 

 per cent, of gold. This result appeared to me to be interesting, 

 as showing that hyposulphite of soda dissolved out a sensible 

 amount of gold from the ore roasted per se. Is it probable 

 that, in the presence of a large excess of other metallic oxides, 

 the gold itself may, at least in a certain proportion, have 

 existed in combination with oxygen ? f 



* Lead free from silver. 



f See a curious paper by Brandt, Recueil des Memoires les plus interes- 

 sants de Chymie, ^-c, dans les Actes de I'Academie d^ Upsal, ^-c. Paris 1764, 

 vol. ii. p. 357. 



