GALENA. 67 



If dissolved in nitric acid, the white sulphate of lead may 

 be thrown down as a precipitate by adding sulphuric acid ; 

 or as chloride of lead by adding hydrochloric acid. 



As, however, other chlorides might be formed at the same 

 time, the precipitate should have ammonia added to it, 

 when, if chloride of lead, it is unaltered. 



Galena (the principal ore of lead). 



Crystallization cubical and cleavable in cubes, also 



octahedral. 

 Lustre shining metallic ; the surface may be dull, but 



the fracture is brilliant. 

 Colour lead grey. 

 Streak lead grey. 

 H. 2-5; S.G. 7-5. 

 Composition when pure, 86-6 per cent, lead, the rest 



sulphur. 



Unless heated carefully in the B.F. it is apt to decrepi- 

 tate, but eventually yields a globule of lead. Can be decom- 

 posed by nitric acid. Galena can be distinguished from silver 

 and other ores by blowpipe and chemical tests as well as 

 by its characteristic cubical cleavage. The ore usually con- 

 tains a perceptible amount of silver, and its presence may 

 be observed by dissolving the ore in nitric acid and dipping 

 a piece of bright copper into the solution, when a silver 

 film will be formed. A galena ore should always be care- 

 fully assayed for silver, as sometimes it is very rich. It is an 

 erroneous notion that fine-grained galena is more argenti- 

 ferous than a coarse-grained one, though it might be in a 

 particular district. Galena is frequently found in gold- 

 Dearing lodes. 



Carbonate of Lead (white lead ore). 

 Often found near surface of a galena lode. 



Compact, earthy, or fibrous masses. 



Crystallization prismatic, &c. 



Structure brittle. 



Lustre glassy or adamantine ; is transparent or trans- 

 lucent, when pure. 



Colour white or greyish (sometimes with a bluish 

 tinge) and often discoloured brown. 



