44 Van Horn — Formulas of Pear cc tie and Polyhasite. 



analysis upon which Hose based his formula, the silver is 

 clearly nearer the smaller value (8*17), while the sulphur is 

 almost as near the smaller quantity as it is the larger (11'524). 

 There is only one analysis which conforms strictly to Rose's 

 formula, namely 7. The remaining analysis, 2, conforms to the 

 larger formula closely with respect to sulphur (1T938), but the 

 silver is again nearer the smaller quantity (S # 470). Therefore 

 the evidence of all previous analyses of polyhasite is over- 

 whelmingly in favor of the formula (Ag,Cn), c (Sl),As) a S n 

 which was first suggested by Rammelsberg in 1875. In addi- 

 tion to the testimony of the combining ratios given above, we 

 also have the undoubted isomorphism of polyhasite with pearce- 

 ite in which the combining ratios conclusively point to the 

 formula (Ag,Cu) 16 (As,Sb) 2 S n . The writer therefore feels that 

 all available evidence logically warrants the acceptance of the 

 smaller formula for both pearceite and polyhasite. 



Geological-Mineralogical Laboratory, 

 Case School of Applied Science, 



Cleveland, Ohio, February, 1911. 



