ORDER ix. IIEXAHEDRAL SILVER. 435 



OBSERVATIONS. 



1. Native Silver has been divided into common and awH. 

 fcrcus native Silver. It is at present impossible to decide 

 whether the latter ought to be united as a variety with 

 the former, or whether it forms a species of its own ; as 

 \ve are not yet sufficiently acquainted with all its physical 

 properties, by which alone this question can be decided. 

 Specific gravity and the yellowish colour form the distinc- 

 tive marks between them ; but as these might be explain, 

 ed by mere mechanical juxtaposition of the two metals, 

 they are ffi)t alone sufficient for this purpose. 



2. The common varieties present the pure silver, as 

 produced by nature, occasionally alloyed with a small pro- 

 portion of antimony, arsenic, iron, &c. A variety of the 

 auriferous native silver yielded to KLAPROTH, and another 

 to FORDYCE, the following ingredients : 



Silver 36-00 72-00. 



Gold 54-00 20-00. 



The hexahedral Silver is soluble in cold nitric acid, but in 

 sulphuric acid only with the assistance of heat. It crys- 

 tallises from fusion*. 



3. Hexahedral Silver occurs principally in veins, tra- 

 versing gneiss, clay-slate, and other primitive and transi- 

 tion rocks. It is accompanied by numerous species of the 

 orders Kerate, Metal, Pyrites, Glance, and Blende, also 

 by rhombohedral Quartz, rhombohedral and macrotypous 

 Lime-haloide, &c. The auriferous native silver, though it 

 is found in the same repositories, is far more scarce. The 

 formation of Black Silver, a black, friable substance, which 

 is very rich in silver, seems to depend chiefly upon the pre- 

 sence of native Silver, or also of hexahedral Silver-glance. 



* A globule of silver melted before the blowpipe, if not too 

 large, forms while crystallising a single individual, in which the 

 faces of the octahedron, the hexahedron, and the dodecahedron 

 may be most distinctly traced, and admit of measurement by 

 the reflective goniometer, but particularly those of the octahe- 

 dron. The surface of the globule appears reticulated. H. 



