282 zinc. 



cinally as an external application to superficial inflammations and 

 excoriations, dusted on the part, and it forms the basis of the com- 

 mon healing cerate. 



Sp. 3. Electric, or Prismatic Calamine. — Prismatischer 

 Zink-Baryt, Mohs.; Zinc oxyde, Hani/. — This species is so called 

 from its becoming strongly electric when gently heated. Its most 

 common colours are white and yellow ; it also occurs green, grey, 

 yellow, and brown. It occurs massive, disseminated, laminar, 

 stalactitic, reniform, botryoidal, cellular, corroded, and crystalized, 

 either in small crystals or in groups scopiformly aggregated like 

 zeolite. The secondary forms are numerous, but, according to 

 Hauy, the octahedron is the primitive form. The lustre is pearly, 

 inclining to adamantine; it varies from transparent to opaque. It 

 yields to the knife, but is harder than calamine. The spe- 

 cific gravity is 3*4. It is infusible ; but dissolves in muriatic acid. 

 Its constituents are oxide of zinc 68*3, silica 25, water 4*4. Smith- 

 son. It is found in small quantities principally along with the ores 

 of lead. 



Sp. 4. Red Zinc Ore. It is of a blood or aurora red colour. It 

 occurs massive and disseminated. The fresh fracture is shining, 

 foliated j the cross-fracture is conchoidal. It is translucent on the 

 edges, or opaque. It is brittle, easily scratched by the knife, and 

 gives a browish- yellow streak. The specific gravity is 6*22. Its con- 

 stituents are zinc 76, oxygen 16, oxides of manganese and iron 8 

 = 100. Brnce. This ore has been hitherto found only in North 

 America, where it occurs in great abundance in several of the iron- 

 mines in Sussex county, New Jersey. 



The most valuable ores of zinc from which the metal is extracted 

 are Calamine and Blende. The ore, after being reduced to small 

 fragments, and separated as much as possible from foreign matter, 

 is commonly roasted, by which the sulphur of the former, and the 

 acid of the latter, are expelled. The product is then washed, in 

 order to separate the lighter matter, and the heavy part which 

 remains is mixed with one eighth of its weight of charcoal. The 

 mixture is next reduced to powder in a mill, in which state it is 

 introduced into the pots or crucibles to be smelted. These pots 

 resemble oil-jars in shape, and are arranged round a circular fur- 



