TUNGSTATE OF LEAD. 165 



ish. Streak white. Transparent . . . translucent. 

 Index of refraction, ord. = 1-43., extr. 1-53. 

 Hardness = 2-5 ... 3-0. Sp. Gr. =5 2-112. 



Compound Varieties. Thin columnar composi- 

 tions of crystals lengthened between M and T ; 

 fracture radiated, owing to the longitudinal distinct 

 face of cleavage. 



The analysis of this mineral by KLAPROTH has been given 

 above, Vol. II. p. 29., agreeing with BERZELIUS formula 

 Na C 3 + 4 Aq, or 37-99 of soda, 40-15 carbonic acid, and 

 21-86 of water. It does not melt in its water of crystalli- 

 sation, and is not altered by the influence of the atmo- 

 sphere. It is formed on the banks of the natron lakes in 

 Sukena, a province of the kingdom of Fezzan in Africa, in 

 the shape of crystalline coats, and occurs also on the surface 

 of the earth. It is exported from thence in considerable 

 quantities under the name of Trona. The natural carbon- 

 ate of soda from the lake of Merida in Columbia, probably 

 also belongs to this species. 



TUNGSTATE OF LEAD. 

 BARYTE. 



Tungstate of Lead. PHILL. p. 350. 



Probably pyramidal. Crystals acute four-sided 

 pyramids and prisms in parallel position, contrac- 

 ted at the ends, and aggregated in bunches. 



Lustre resinous. Colour yellowish-grey. Faintly 

 translucent. 



Before the blowpipe it melts and gives off vapours of 

 lead, leaving a crystalline globule of a dark colour and met- 

 allic aspect, which yields a pale grey powder. When the 

 lead has been driven off, it yields with borax a yellow 



