()?i Mbieral Substances. 273 



only dissolved the added silver, and left- the original twenty- 

 five grains of electrum untouched. 



c. It was then melted with thrice its weight of silver, lami- 

 nated, and digested in nitric acid, which now effected, a complete 

 separation, leaving the gold in heavy brown scales, which being 

 washed, and fused into a button, weighed 16 grains, 



d. The silver was separated from the nitric solution by the 

 immersion of a plate of copper, and amounted to 84 grains : 

 deducting the 75 grains, which were added, 9 grains remain as 

 the proportion of that metal contained in the native alloy ; 

 hence the electrum consists of gold 64 grains 



silver 36 . . 



100 

 As this alloy resists the action of nitric, and even of nitro- 

 muriatic acid, it is evidently not a mere mixture of gold and 

 silver, but a peculiar definite ore in which those metals are 

 chemically combined. 



2. Chemical Analysis of the Pacos, or red Silver Ore of Peru. 



I am indebted to M. von Humboldt for the specimen of the 

 Peruvian silver ore, which is called pacos, employed in these 

 experiments. When minutely examined, it has the appear- 

 ance of a brown oxide of iron traversed by filaments of native 

 silver, which is therefore easily separable by amalgamation. 



a. 100 grains of this ore heated to redness lost 8.5 grains, 

 and acquired a brown red colour. 



b. 200 grains digested in nitric acid furnished a colourless 

 solution, when filtered, from which muriate of soda threw 

 down 37.25 grains of muriate of silver, equivalent to 28 grains 

 o{ metaWic silver . The remaining liquid supersaturated by car- 

 bonate of potassa, afforded a light brown precipitate of oxide of 

 iron, which after ignition weighed three grains. 



c. The portion which had resisted the action of nitric acid 

 was digested in boiling muriatic acid ; nine grains remained 

 undissolved, consisting of seven grains of impalpable siliceous 

 earth and two grains of coarse sand, amongst which minute 

 octoedral crystals were perceptible, consisting probably of fer- 



