260 



METALS. 



with clay ; into this liquid the earthen vessel is dipped and 

 then baked. 



Cuproplumbite is a galena containing 245 per cent, of sulphuret of 

 copper. From Chili. 



ARSENURETS, SELENIDS, AND TELLURIDS OF LEAD. 



These various ores of lead are distinguished by the fames before the 

 blowpipe, and by yielding ultimately a globule of lead. 



Cobaltic lead ore is an arseniuret of lead, containing a trace of cobalt 

 From the Hartz. Gives an alliaceous odor (from the arsenic) befor 

 the blowpipe. Gr=8*44. 



Dufrenoysite is an arseniuret and sulphuret of lead ; in dodecahe 

 drons of a dark steel-gray color. Gr=555. From the Dolomite of St 

 Gothard. 



Clausthalite, or selenid of lead, has a lead-gray color, and granular 

 fracture. Gr=719. Gives a horse-radish odor (that of selenium) be- 

 fore the blowpipe. From the Hartz. There are three selenids of lead 

 and copper which give the reaction of all the different constituents be- 

 fore the blowpipe. The sp. gr. of one is 5*6 ; of tbe second 70 ; the 

 third 74. From the Hartz. There is also a selenid of lead and mer- 

 cury occurring in foliated grains or masses, of a lead-gray to bluish and 

 iron-black color. 



Tellurid of lead. This is a tin- white cleavable mineral. Gr=8"16. 

 From the Altai mountains. 



Foliated tellurium is a less rare species, remarkable for being foli- 

 ated like graphite. Color and streak blackish lead-gray. H=l — 1*5. 

 Gr=7085. It contains tellurium 32-2, lead 54*0, gold 90, with often 

 silver, copper, and some sulphur. From Transylvania. 



minium. — Oxyd of Lead. 



Pulverulent. Color bright red, mixed with yellow. Gr= 

 4*6. It is a sesquioxyd of lead. Affords globules of lead 

 in the reduction flame of the blowpipe. 



Obs. Occurs at various mines, usually associated with 

 galena, and is found abundantly at Austin's mines, Wythe 

 county, Virginia, with white lead ore. 



Uses. Minium is the red lead of commerce : but for the 

 arts ft is artificially prepared. Lead is calcined in a rever- 

 beratory furnace, and a yellow oxyd (massicot) is thus 

 formed : the massicot is afterwards heated in the same fur- 

 nace in iron trays, at a low temperature, by which the lead 

 absorbs more oxygen and becomes red lead. A much better 

 material is obtained by the slow calcination of white lead. 



Plumbic ocher is another similar ore, of a yellow color ; it is a pro* 

 toxyd of lead. Occurs in Wythe county, Va., also in Mexico. 



What is minium ? What are its characters 1 



