1814.] On the Composition of Blende. 91 



graaf does not expressly mention the presence of sulphur in this 

 mineral ; though from his treatment of it, and his description of 

 the process, it follows clearly, 1 conceive, that lie was acquainted 

 with its existence. Cartheuser, in his Mineralogy, published in 

 1J55, says, that besides zinc and sulphur it contains iron and 

 arsenic* In 1 77*^? Bergman published a chemical analysis of 

 the ores of zinc, lie examined many varieties of blende, and 

 found them composed of zinc, iron, sulphur, arsenic, alumina, 

 and silica, f 



The French chemists, after the introduction of the Lavoisierian 

 theory, relying upon the difficulty of uniting zinc and sulphur 

 together by heat, considered blende as a sulphurcted oxide of zinc. 

 This opinion was first called in question by Proust, who having 

 analysed some specimens of that ore, found that the zinc must 

 exist in it in the metallic state. J An analysis of brown blende, 

 which I made soon after, induced me to adopt the same conclu- 

 sion^ The analysis of Dr. Kidd leads directly to the same opi- 

 nion, and indeed is inconsistent with any other. I believe it is 

 generally received at present both by chemists and mineralogists : 

 hence if blende be a sulphuret of zinc, an accurate analysis of it 

 would make us acquainted with the proportion in which sulphur 

 and this metal combing, which has not yet been determined by 

 satisfactory experiments. There can be no doubt, from the table 

 of sulphurets given in the second volume of the Annals of Philo- 

 sophy, that an atom of all the metals either combines with one 

 atom or with two atoms of sulphur. But though blende was found 

 in that table to approach to a compound of one atom zinc and one 

 atom sulphur, it did not exactly agree with the weights of these 

 atoms as determined by other data. This want of coincidence 

 might be owing to errors in the analysis of blende, or to mistakes 

 into which 1 had fallen in determining the weight of an atom of 

 zinc. In order to ascertain this point, and likewise to see whether 

 the iron which blende contains exists in the state of an oxide or 

 metal, and whether it be combined with sulphur, I made several 

 very careful analyses of that ore, and was not satisfied till 1 ob- 

 tained the exact weight of the blende originally employed, which, 

 is much more difficult than those not conversant in chemical ana- 

 Id imagine. 



Werner describes three subspecies of blende, distinguished from 

 each other chiefly by their colour, namely, the yellow, brown, and 

 black. I have not yet subjected black blende to analysis; bin I 

 find thai the yellow and the brown subspecies agree nearly in their 

 composition. The only difference is that the brown contains more 

 iron than the yellow. 1 have never analysed any yellow blende 

 perfectly free from iron. The purest specimen 1 have met with 

 contained I j per cent, of that metal, while specimens of brown 



* Cnrlhi Ineralogy, p, dl, t Opuc. il. 820. 



• 'our. etc Pliyi. hi. 79. ', JmneicVi Mineralogy, ii. 



