a new Mineral Species from Chile, 425 



On quantitatively analysing the mineral, the following results 

 were obtained : — 



In the Analysis A the arsenic was determined from the amount 

 of arseniate of magnesia and ammonia, previously dried at 2 12°F., 

 obtained by dissolving 11 -01 grs. of the mineral in nitrohy- 

 drochloric acid, supersaturating with ammonia, and afterwards 

 adding chloride of magnesium along with chloride of ammonium. 

 The silver was determined by cupellation, and the copper reck- 

 oned as loss. 



In the Analyses B, C, and D, the silver was, as before, esti- 

 mated by cupellation with lead; but the arsenic, on the con- 

 trary, was reckoned as loss after determining the copper present 

 by the blowpipe as follows : — 



From 1 to 2 grains of the mineral were fused upon charcoal 

 in reducing flame along with a very small amount of borax- 

 glass and a previously tared globule of pure gold, the globule of 

 gold being from 3 to 4 grains in weight : when perfectly fused, 

 the united globule was separated from the adherent borax-glass 

 by dipping it into water after solidification, but whilst still hot, 

 This globule was then placed in a charcoal bore, and, after fusion, 

 very carefully treated with a gentle oxidating flame as long as 

 arsenical flames were evolved, and until the instant when the 

 greenish appearance peculiar to melted copper when pure was 

 observed, when it was found to have eliminated all the arsenic, 

 and there remained a perfectly malleable red metallic button of 

 an alloy of gold and copper, the weight of which, less that of the 

 globule of pure gold added, gave the amount of copper and silver 

 present in the ore; and deducting from this the proportionate 

 quantity of silver found by cupelling with lead a separate portion 

 of the mineral, the quantity of copper present was ascertained. 



The results obtained by this method are very accurate ; and it 

 can frequently be used with advantage in determining copper in 

 compounds of this metal with arsenic when free from sulphur. 

 Iron and gangue do not affect its accuracy, as they are slagged 

 off easily in the fusion with borax-glass. In the assay of mala- 

 chites and oxides or silicates of copper, the copper present can 

 easily be brought to the state of an arsenide by a previous opera- 

 tion, and then determined as above. 



The results above stated leave no doubt that the constitu- 

 tion of this mineral may be represented by the formula Cu 18 As, 



Phil. Mag. S. 4. Vol. 20. No. 135. Dec. 1860. 2 F 



