Native Seleniuret of Lead and Stdphiiret of Selenium. 221 



Hartz, to Professor Hausmann, with the observation that it 

 contained selenium. It was found some years since in the St. 

 Lawrence mine near Clausthal ; and M. Bauersachs, who at 

 that time regarded it as a distinct species, termed it cobaltic 

 galena; under which name Professor Hausmann introduced it 

 into his Mineralogy. The mineralogical description of it, as 

 given by Professor Hausmann, is as follows : Extei-nally it 

 bears considerable resemblance to fine granular galena, though 

 its colour is clearly different, having a cast of blue like molyb- 

 dena. A crystalline texture is quite distinct, but from the 

 minuteness of its crystals it has hitherto been impossible to 

 ascertain their precise form. Cubic and triangular surfaces 

 were observed ; but whetlier they correspond or not to those 

 of galena could not be determined. A similar remark applies 

 to its cleavages, of which there appear to be several. It is less 

 hard than galena ; and its density is 7*697. It becomes ne- 

 gatively electric from friction, like galena. It is readily de- 

 composed, before the blowpipe, on charcoal. Besides the 

 usual pha3nomena arising from the presence of lead, the odour 

 of decayed horseradish may be perceived ; and a reddish- 

 brown matter is deposited round the assay on the cool parts 

 of the charcoal. The ore shines with a clear blue light 

 while the blowpipe flame is playing upon it. It communicates 

 a pale-blue colour to borax, indicative of a little cobalt. When 

 heated by means of a spirit-lamp, in a clear glass tube 

 closed at one end, the selenium almost instantly sublimes, 

 forming a red ring within the tube, at the open extremity of 

 which its peculiar odour is very perceptible. On heating the 

 tube to redness, the ore fuses, the red ring partially disappears, 

 and is succeeded by a white crystalline deposit. This deposit 

 reddens litmus paper, is deliquescent, and has all the proper- 

 ties of selenic acid. These characters, which I have myself 

 witnessed on a specimen sent me by Professor Sti'omeyer, 

 are very distinct. Nitric acid acts readily upon the ore even 

 in the cold. The lead is first attacked, the selenium sepa- 

 rating in substance in red flocculi : by the aid of the heat 

 these also are oxidized, selenic acid being generated. The 

 solution, when complete, has a pale rose-colour, owing to the 

 presence of cobalt ; but the nicest test could detect neither 

 sulphuric acid nor any other substance. The analysis was 

 performed by the following method: — After dissolving the ore 

 completely in nitric acid, the oxide of lead was precipitated by 

 sulphuric acid, the operation being conducted at a boiling 

 temperature, to prevent the precipitation of any seleniate of 

 lead. Tlie filtered solution was then concentrated by eva- 

 poration, and selenium thrown down by sulphate of ammonia 



and 



