108 Mr. D. Forbes on the Chemical Composition 



• 



none of them were found to contain arsenic in true combination 

 with the silver. 



One specimen from the Retamo, north-east of Copiapo, was 

 native silver in coarse interwoven threads, which upon inspection 

 appeared to be regular octahedrons, as it were drawn out and 

 elongated until their length equalled some fifteen times the 

 measure of their short axis. Upon assay they yielded 99 "86 

 per cent, silver. 



Another specimen from Punta Brava, also near Copiapo, 

 proved to be native arsenic massive, but curiously w r oven 

 through, if the term may be used, with wonderfully fine fila- 

 ments or threads of native silver free from arsenic. 



When examining the Mina Marguarita at Bandurias near 

 Chanarcillo, I found, however, a peculiar dull grey mineral, 

 semi-malleable, and which, on burnishing, received an almost 

 silver-white polish, situated in quartz, in which it occurred as 

 small grains or plates associated with smaltine. All the speci- 

 mens I obtained appeared too impure to be then considered 

 worthy of a quantitative analysis, but on examination by the 

 blowpipe they gave a strong reaction of arsenic, and left a globule 

 of silver behind on the charcoal. 



Lately Domeyko has examined a mineral also from Bandu- 

 rias, but mine not specified, which is stated to occur in a matrix 

 of white argillaceous carbonate of lime, and in colour to vary 

 from lead-grey to tin-white. Upon pulverizing the specimens, 

 they were found to consist of a mixture of several metallic mine- 

 rals independent of the gangue. A ductile mineral in granules 

 flattened by the blows was easily separated from the more pul- 

 verizable portion, which in turn, by means of washing, was again 

 separated into a heavy metallic powder, and a lighter, black, 

 earthy-looking sediment. 



These three products have been separately analysed by Do- 

 meyko, who, however, has contented himself with, stating the 

 numerical results of his analyses, without speculating as to their 

 possible chemical constitution. The results obtained were as 

 follows : — 



Metallic granules. Metallic powder. Black sediment. 



Silver . . 



. 82-5 



39-8 



1-50 



Mercury 



5-6 



— 



— 



Iron . . 



0-3 



13-8 



1-90 



Cobalt . 



. 0-6 



8-3 



11-55 



Nickel . 



— 



06 



3-75 



Arsenic . . 



. 10-1 



27-1 



53-70 



Antimony . 



. 0-8 



10 



— 



Sulphur 



— 



— 



0-15 



Gangue 



— 



8-2 



26-50 





9^9 



98-8 



99-05 



