DR T. THOMSON on the Composition of Blende. 333 

 that it was composed of 



Sulphur, . 29 



Arsenic, 1 



Water, 6 



Lead, . 6 



Iron, . 9 



Zinc, 45 



Silica, 4 



100* 



But his mode of analysis was so bad, that it is obvious he could 

 draw no legitimate conclusion respecting the constitution of 

 blende from his experiments. 



About the beginning of the present century, it was generally 

 admitted by chemists and mineralogists, that blende is a sul- 

 phuret of zinc. But the unsuccessful attempts to combine sul- 

 phur and zinc together by heat, induced MORVEAU to beh'eve 

 that the zinc in blende was in the state of oxide. PROUST, how- 

 ever, showed, that when blende is mixed with charcoal, and ex- 

 posed to a red heat, no sulphurous acid whatever is given offf ; 

 which led him to conclude, that in blende the zinc is in the me- 

 tallic state. This opinion, in consequence of the progress which 

 chemical science has made, has been for these twelve or fourteen 

 years universally adopted. Though I am not aware of any mo- 

 dern chemist who has attempted to determine the proportions 

 of its constituents with rigid accuracy except ARFWEDSON, who 

 has given us an analysis of a very pure specimen of blende in 

 the Memoirs of the Stockholm Academy for 1822, p. 438. 



ARFWEDSON employed for his analysis yellow-coloured and 



Opusc. ii. 330. f Jour, de Phys. Ivi. 79. 



Tt 2 



