354 palmer: bornite as silver precipitant 



Per cent 



63.4 = 0.962 



Dissolved copper 61 .00 



Free silver 100.9 4- 107.9 = 0.935 



Combined silver 101.8 -^ 107.9 = 0.943 



and 



Free Combined 

 Copper silver silver 



0.962 : 0.935 : 0.943 = 1.00 : 0.97 : 0.98 



This experiment shows that for every atom of copper dissolved 

 by the silver sulphate solution one atom of free silver and one 

 atom of combined silver in the residual material are deposited. 

 It is apparent, therefore, that the copper of this bornite is cuprous 

 just as it is in chalcocite and to express the cuprous nature of the 

 copper it is convenient to use for this bornite the formula 

 SCuoS.FeoSs after the dualistic system. This formula may be 

 considered a constitutional formula for the mineral under ex- 

 amination, and its corresponding molecular formula becomes 

 CuioFe2S8. 



The proportional amounts of the substances participating 

 in this reaction of bornite may, therefore, be expressed by the 

 equation : 



CuioFeoSs + 10AgoSO4 = lOAg + Ag^oFcsSs + IOCUSO4 



Thus one gram of this bornite is capable of precipitating 2.15 

 grams of silver as silver and silver sulphide. In strong contrast 

 with the reactivity of its cuprous constituent is the inertness of 

 the sulphoferric portion of the bornite. 



Inasmuch as the group, Fe^Ss, is not known to exist as an inde- 

 pendent mineral, the formation of a silver ferric sulphide as one 

 of the products of the reaction of bornite with silver sulphate 

 solution may be presumed. Moreover, from the stability of 

 the compound residual products it seems not improbable that 

 in regions abounding in silver deposits associated with bornite 

 some silver sulphoferric mineral as a secondary product may 

 yet be found. It is hoped that further study of the conduct 

 of copper iron sulphide minerals with silver salt solutions will 

 shed light on the chemical relations which sternbergite and its 

 allied minerals bear to one another. 



