tin. 159 



Zinc is a brittle metal, but admits of being rolled into sheets when 

 heated to about 213° F. In sheets it is extensively used for roofing 

 and other purposes, it being of more difficult corrosion, much harder, 

 and also very much lighter than lead. It is also employed largely for 

 coating (that is, making what is called galvanized) iron. Its alloys with 

 copper ( page 144) are of great importance. 



The white oxide of zinc is much used for white paint, in place of 

 white lead ; and also in making a glass for optical purposes. 



An impure oxide of zinc, called cadmia, often collects in large quan- 

 tities in the flues of iron and other furnaces, derived from ores of zinc 

 mixed with the ores undergoing reduction. A mass weighing 600 

 pounds was taken from a furnace at Bennington, Vt. It has been ob- 

 served in the Salisbury iron furnace, and at Ancram, in New Jersey, 

 where it was formerly called Ancramite. 



CADMIUM. 



There is but a single known ore of this rare metal. It is 

 a sulphide, and is called Greenochite. It occurs in hexagonal 

 prisms, with dissimilar pyramidal termination, of a light 

 yellow color, high lustre, and nearly transparent. H. =3- 

 3*5. G. =4-8-5. From Bishopton, Scotland. 



Cadmium is often associated with zinc in sphalerite and 

 calamine. The cadmiferous sphalerite is called Przibramite. 



The metal cadmium is white like tin, and is so soft that 

 it leaves a trace upon paper. It fuses at 442° F. It was 

 discovered by Stromeyer in 1818, 



TIN. 



Tin has been reported as occurring native in the gold 

 washings of the Ural, and in Bolivia. There are two ores, \/ 

 a sulphide and an oxide. It also occurs in some ores of 

 columbium, tantalum, and tungsten. 



Stannite.— Tin Pyrites, Sulphuret of Tin. Tin Sulphide. 



Commonly massive, or in grains. Color steel-gray to iron- 

 black ; streak blackish. Brittle. H. =4. G. =4-3-4-6. 



Composition. Sulphur 30, tin 27, copper 30, iron 13 = 100. 



Obs. From Cornwall, where it is often called bell-metal 

 ore, from its frequent bronze appearance ; also from Ireland 

 and the Erzgebirge. 



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