CERTAIN INTERESTINa CRYSTALLINE ALLOYS. 



By RICHARD PBARCE, Dbnveb, Col. 

 (Extracted from the Transactions of the American Institute of Mining Engineers.) 



In" tlie treatment of auriferous copper containing bismuth, I 

 have recently observed a small quantity of a grayish- white alloy, 

 which on examination, proved to be Bi containing in solution, as 

 it were, a crystalline alloy of Bi and Au. This compound makes 

 its appearance on the surface of the auriferous Cu in small 

 globules as the latter cools. 



These globules are rapidly attacked by nitric acid, and fine 

 needle shaped crystals of Bi and Au separate out. They are 

 insoluble even in strong nitric acid. 



On examination, the crystals were found to contain : Gold 

 69.94 per cent.; silver, 0.63 per cent.; bismuth, 29.43 per cent. 

 (No. 1).* 



The residue is very fusible, and at a temperature consider- 

 ably below its melting-point it oxidizes rapidly, changing from 

 its original gray color to a greenish-yellow (No. 2). On melting 

 in a crucible under flux, a bronze-colored alloy is formed that has 

 a specific gravity 15.47 — somewhat higher than the calculated 

 specific gravity of a simple mixture of the two metals in the pro- 

 portions named. 



In following out my investigations by repeated examinations 

 of this alloy, formed at different times, I found that, in dissolving 

 a miscellaneous lot of the alloy in nitric acid, some gold-yellow 

 crystals were formed, which I succeeded in separating from the 

 BiAu alloy by washing. These yellow crystals, under the 

 microscope, showed distinct, regular, octahedral faces, and on 

 examination they were found to be a crystalline alloy of Au and 

 Ag in the proportion of 69 Au, 21 Ag (No 3). The quantity 

 was too small to admit of any very correct determinations of 

 these crystals ; but the peculiar feature was remarked that they 

 contained Ag, while the BiAu crystals did not in any appreciable 

 quantity. 



* This and similar numbers following refer to the samples forwarded by the 

 author to the Secretary. 



