DR T. THOMSON on the Composition of Bknde. 335 



1.811, and was pure, with the exception of a trace of iron. 

 1.311 oxide of zinc, according to BERZEHUS'S tables, are equiva- 

 lent to 1.05 metallic zinc. Thus, by ARFWEDSON'S analysis, 

 1.758 blende are composed of 



Zinc, ...... 1.167 or 66.382 



Sulphur, . . 0.592 33.675 



1.759 100.057 



When we correct ARFWEDSON'S analysis by my formula?, 

 which I consider as more accurate than those of BERZELIUS, the 

 result is as follows : 



Zinc, . . . 1.17947 or 67.091 

 Sulphur, . . 0.58523 33.290 



1.76479 100.381 

 Now, this is equivalent to 



Zinc, 4.25 



Sulphur, 2.1087 



4.25 is the atomic weight of zinc. But 2.1087 exceeds 2 

 (= atom of sulphur) by rather more than ^th of an atom. Con- 

 sequently, if ARFWEDSON'S analysis be correct, blende is not a 

 simple combination of an atom of zinc and an atom of sulphur, 

 but contains an excess of this last substance. 



There are two circumstances connected with ARFWEDSON'S 

 analysis that prevent me from trusting implicitly in its accu- 

 racy. 



1. The 0.393 of matter which did not dissolve in aqua regia, 

 must have been dried at a very lo\v heat, because sulphur begins 

 to sublime at a temperature considerably under that of boiling 



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