Natural Hijtory cf Zinc. [Book VI. 



Zinc is found in the following flares : It is fome- 

 times, though rarely, difcovered native in flexible, 

 greyifh, and inflammable fibres. Zinc in its ore is 

 generally in the form of a calx; when the ore contains 

 no other metal but zinc it is never in any other form, 

 but it is often mixed with other ores, which contain 

 iulphur and arfenic, and thefe mud be evaporated by 

 roafting. The richefr. ores are compact and ponde- 

 rous, and are called lapis calaminaris, or calamine ; 

 they are found in the parifh of Holywell, in Flint- 

 Ihire. 



Margraff has afcertained the quantity of zinc con- 

 tained in different forts of calamine : 



Parts. Parts. 



Calamine, from near 7 



Cracow J l6 8 ave - zmc - 



Calamine, from England 16 3 



from Breflaw 16 4! 



: from Hungary 16 i\ 



from Holywell 16 7 



In one hundred pails of lapis calaminaris were found 

 eighty-four of calcined zinc, three of calcined iron, 

 about one of pure clay, and twelve of filiceous earth, 

 according to Bergman. 



There is another fpecies of mineral ufed in making 

 brafs called blende, mock lead, or black jack, which 

 ccnfifts of zinc mineralized by fulphur, and fornetimes 

 by iron. 



The method of making ordinary brafs is as follows : 

 Copper in thin plates, or, which is better, copper 

 reduced (by being poured when melted into water) 

 into grains of the fize of large fliot is mixed with cala- 

 mine and charcoal, both in powder, and expofed in a 

 melting pot for feveral hours to a fire not quite ftrong 



enough 



