1S14.] On the Composition of Blende. 89 



Number of Weight of an 



i atoms. integrant particle. 



294 Peroxide of titanium 1 t + 2 o... .20*010 



295 Protoxide of rhodium 1 rk + 1 o . . . . 1 5*90:5 



296 Deutoxide of rhodium 1 r'l + 2 o.... 16-303 



29/ Peroxide of rhodium 1 rh + 3 o . . . . iy-903 



These are all the alterations and additions which I can venture at 

 present to make upon my original tahle, puhlished in the first 

 number of the second volume of the Annals of Philosophy. I 

 have prefixed numbers to all the additional substances introduced in 

 the present table, partly for the sake of easy reference, and partly 

 that the reader may be able at a glance to distinguish those bodies 

 the weights of whose atoms have been altered. I am far from con- 

 ceiving that, even with these alterations, I have attained to any 

 thing like precision ; but it is only by constant corrections that we 

 can expect, in such a science as chemistry, to approximate at last 

 sufficiently near the truth for all practical purposes. 



Article III. 



On the Composition of Blende. By Thomas Thomson, 

 M.D. F.R.S. 



As far as is known at present, zinc, though a verv abundant 

 metal, enters into a much smaller number of mineral combinations 

 than lead or copper or even silver, it lias been found only in four 

 states constituting the four following species: 



1. Blende. 



_'. Hydrous carbonate of zinc. 



3. Anhydrous carbonate. 



4. Silicated zinc. 



In the hist three of these species, which are usually confounded 

 ither under the name oi calamine, the zinc is in the state of 

 an oxide ; but in blende it occurs in the metallic state. 



Mr. Smithson, some years ago, determined the composition of 

 the last three species of the ores of zinc with sufficient accuracy. 

 But if we except the experiments of Bergman, made in 1 7 7 f>, 

 when chemical analysis had not acquired the requisite exactness to 

 decide upon the composition of complicated minerals, and a single 

 hy Dr. Kidd, published two or three years ago, we are not 

 In possession of any well established facts respecting the composi- 

 tion of blende. On that aeeount, 1 conceive it will be worth 



while to lay before the public the result of some experiments 

 which I made lately, in order to satisfy myself upon this point. 



Blende i-. an ore of zinc, which almost always accompanies 

 galena ur sulpburet of lead, and which by the English miners is 



