particularly thofe ofZ'mc and Cobalt. 1<,X 



fince the attentive naturalift is fufficiently taught, by expe- 

 rience, that in the mineral kingdom fubftances of the fiimc 

 genus, though different in external form, confift often of the 

 fame component parts ; and that other bodies of the like 

 kind differ in their component parts, though perfectly alike 

 in their external appearance. As this is the cafe, we can 

 find no better guide to conduct us to an invariable claflifica- 

 tion, arrangement, and definition of mineral bodies than 

 chemiftry ; a knowledge which muft be united with that of 

 the external charafters of minerals. 



To oive an inftance of the uncertainty which arifes when 

 thefe are feparated, I {hall here mention thofe ores which 

 are known bv the name of cadmia ; for it would fcetn, by 

 the many improper denominations which are often founded 

 on their external charaftcrs, as if we were almoft conducted 

 back to the dark age of Cadmus, from whom the Europeans 

 are faid to have firft learnt the art of fufing ores on a large 

 fcale, and from whom, in all probability, the term cadvila 

 had its origin. In this refpeft chemical knowledge is a 

 better jruide than external chara6lers, and the names thence 

 deduced, and often very improperly ; it enables us to define 

 minerals with more accuracy, and condufts us nearer than 

 the latter to the real knowledge of nature in this department, 

 without which all mineralogical knowledge muft be uncer- 

 tain and imperfeft. As it would be fuperfluous to fay more 

 on this fubjeA, I fhall, for the prefcnt, confine myfelf to the 

 cudmias, and thofe ores alone which, when dccompofed in 

 a proper manner, and fully purified, vicld thofe metals called 

 ^inc and cobalt. 



0/ZiN-c. 

 Ores that contain zinc are found in numerous varieties 

 md of diflerent forms. Sometimes they are combined with 

 oxygen and the fulphurie acid ; and fometimes there are 

 found in them, befides zinc, various foreign component 

 parts, fuch as argil and filiccQus earth, a little iron, lead, 



