J40 PHYSIOGRAPHY. 



with traces of lime, manganese, and animal matter. Ac- 

 cording to KLAPROTH, the variety from Saxony is infusible 

 before the blowpipe, and consists of alumina 63-75, silica 

 29-50, and protoxide of iron 6-75. 



It occurs in several countries in granite ; at Schneeberg 

 in Saxony, in Salzburg, in Auvergne, in Cornwall, in 

 North- America, &c. 



PLOMBGOMME. 



Plomb hydro-alumine (Plomb gomme). HAUY. Traite', 

 2de Ed. T. III. p. 410. 



Reniform. Surface smooth. Composition thin co- 

 lumnar ... impalpable. 



Colour yellowish- and reddish-brown, striped. 

 Translucent. 



Scratches octahedral Fluor-haloide, but does not 

 affect glass. 



If rubbed in an isolated state, it acquires a strong nega- 

 tive electricity. If quickly heated before the blowpipe, it 

 decrepitates and loses its water ; but is infusible by itself. 

 With borax it yields a transparent colourless glass, without 

 reduction of the lead. According to BERZELIUS, it con- 

 sists of 



Oxide of Lead 40-14. 



Alumina 37-00. 



Water 18-80. 



Sulphurous Acid 0-20. 



Lime and the Oxides of i 

 Iron and Manganese J 



Silica 0-60. 



It occurs at Huelgoet near Poullaouen in Brittany, in 

 clay-slate, along with hexahedral Lead-glance, dodecahe- 

 dral Garnet-blende, hexahedral Iron-pyrites, and di-pris- 

 matic Lead-baryte. 



