W. M. Bradley — New Silver-Tellurium Mineral. 165 



It is generally recognized that the formulge of inter-metallic 

 compounds cannot be rationalized on the basis of our common 

 ideas of valence. The silver-tellurium system has been worked 

 out by the customary thermal-micrographic method. Guertler* 

 in his handbook on metallography reviews the work of vari- 

 ous authors, principally Pellini and Quercigh, and concludes 

 that there are two compounds in the series, namely, Ag 2 Te, 

 which is identical with the isometric hessite, and a compound 

 of questionable character, viz. AgTe or Ag 2 Te 3 . Abnor- 

 malities in the equilibrium relations interfere with the exact 

 determination of this formula. Guertler, however, regards 

 AgTe as the more probable one. This compound is formed 

 by reaction between Ag 2 Te and the liquid at 444°. It under- 

 goes polymorphic transformation at 412°. There is no inter- 

 crystalline solubility throughout the entire series, or in other 

 words no solid solution. The natural mineral empressite, 

 which corresponds very closely to the atomic ratio Ag : Te, 

 exhibits a structure wholly in conformity with the conclusions 

 stated above. Upon metallographic examination of a polished 

 section it was found to be a structurally homogeneous sub- 

 stance, showing large irregular light and dark polygonal grains 

 with no interstitial matter. It thus appears to be a definite 

 compound with the formula AgTe. 



In conclusion the author wishes to express his thanks to 

 Professor George, who so kindly furnished the material that 

 made this investigation possible, and also his indebtedness to 

 Professor C. H. Maihewson of the Sheffield Scientific School, 

 who made the metallographic examination. 



Mineralogical Laboratory of the Sheffield Scientific School 



of Yale University, New Haven, Conn., June 3, 1914. 



*Vol. I, Part II, 924-926. 



Am. Jour. Sci.— Fourth Series, Vol. XXXVIII, No. 224.— August, 1914. 

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