288 M. Rose*5 Analysis of the [Oqt. 



that of iron pyrites, and may be called cohaltiferous selenittret of 

 lead,, 



3. Svkniurct of Lead with Seieniurel oj' Copper, — Two Sj^^eci- 

 mens of the minerals sent by M. Zinken were externally pvec^sQlv 

 alike. They were of a lead grey colour, not crystallized; had a 

 saccharoidal fracture, and were composed of nearly homo*;euc- 

 Qus masses. They were surrounded by magnesian carbonate of 

 lime, but not, as seleniuret of lead generally is, disseminated 

 through it. The two specimens were distinguishable from each 

 Sother by the difference in their behaviour before the blowpipe. 

 Both fuse pretty easily on charcoal in a small matrass, but one 

 more readdy than the other. The least fusible melts like sul- 

 phuret of antimony by the heat of a small spirit lamp. In other 

 respects, they behave alike before the blowpipe. They give n<> 

 sublimate when heated in a small matrass, but in an open tube 

 they afford, hke seleniuret of lead, both selenium and selenic 

 acid. The assay fuses, and is surrounded by yellow oxide of 

 lead. With the fluxes they give very distinct trace" of cojiper. 



The least fusible was analysed by chlorine, like the other 

 seleniurets. The fixed chlorides were dissolved in water, and 

 the oxide of lead was precipitated by sulphuric acid, with the 

 precautions detailed in the analysis of the cohaltiferous selenii|(- 

 ret of lead. The solution from which the lead was separated 

 yv'as mixed with caustic potash, and boiled to throw down allthfe 

 i)Xide of copper. The analysis of this mineral gave in 100 partsj 



Selenium... v^*-ij^.fkw<ii29*^6 - 



Iron, with a trace of lead 0*44 



Lead .:;.^?V'69-67 



Iron .V. .-.'I -0*33 



'opper 7'8<5 



Tndecomposed mineral I'OQ 



Loss ......:. 0''74 



100-00* 



*^, S9*67 of lead combine with 22*86 of selenium to form sele- 

 tiiutet of lead. If we suppose the copper to be combined with 

 an atom of selenium, the 7*86 would require 4*93 of selenium", 

 which leaves an excess of selenium. If we imagine the copper 

 to be combined with two atoms of selenium, as in the seleniuret 

 bf copper which is formed by passing seleniuretted hydrojjen 

 into solutions of Oxide of copper, the 7*86 would require 9*86 of 

 selenium, in which case there is a deficiency of selenium. ^ It 

 appears probable, therefore, that the copper exists in the mineral 

 aj» a seleniuret and a biseleniuret, and that the two bear a siinple 



'♦ The solution of the mineral in nitric acid gave no precipitate with muriate, ^^f 

 iJ^rytes; consequently it contains neither sulphur nor sjjjj^^^, ,^ g.uu3pT nw ; 



tJi 



