36 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



(3) Clean sla<;, from the first smelting for matte. (55961.) 



(4) Clean slag, crystallized. (55960.) 



(5) Slag, coated with moss copper. (55962.) 



Second fusion. 



(1) Furnace charge, mixture of first matte with rich siliceous silver ores. (55964.) 



(2) Second matte, produced by smelting No. ,55964. Contains 60 per cent, of cop- 

 per. (55965.) 



(3) Matte, containing 50 per cent, of copper, similar to No. 55965, but produced by 

 a single fusion at the Boston and Montana Smelter, Butte, Montana. (55966.) 



Ziervogel process. 



(1) Second matte, roasted and ground, ready for fine roasting for the production 

 of sulphate of silver. (55967.) 



(2) Silver, precipitated on copper plates from solution of sulphate of silver from 

 No. 5.5967, after roasting for sulphate. (55969.) 



(3) Residue, after leaching out sulphate of silver. (.55968.) 



Third fusion. 



(1) Furnace charge, mixture of leached residues with rich sulphureted gold ores. 

 (55970.) 



(2) Matte, from smelting No. 55970. (55971.) 



Copper fusion. 



(1) Pimple metal, from treatment of No. 55971. Contains 75 per cent, copper and 

 100 ounces of silver per ton. (55972.) 



(2) Pimple metal, calcined and ground. (55973.) 



(3) Oxide of copper. Contains 90 per cent, of copper. (55974.) 



LEAD. 



Lead Minerals, 

 galenite. (galena.) 



Composition : PbS. Sulphide of lead, containing lead 86.6 per cent, 

 and sulphur 13.4 per cent. 



It crystallizes in the isometric system, es{)ecially in cubes with mod- 

 ifying faces. Its most common occurrence is crystalline granular, 

 varying from impalpable to very coarse. One of its most marked char- 

 acters is its perfect cubic cleavage, which shows distinctly whenever a 

 piece is broken, and frequently makes it very friable. It varies in 

 hardness from 2.5 to 2.75, and in specific gravity from 7.25 to 7.7, has a 

 lead-gray color and full metallic luster, occasionally tarnishes, and 

 sometimes shows iridescent colors on the surface. 



Galenite is the most common and abundant of the lead minerals and 

 is undoubtedly the original lead mineral. Wherever exposed to decora- 

 posing influences it changes rapidly and frequently occurs coated with 

 its decomposition i)roducts, since they are mostly insoluble, 



