palmer: bornite as silver precipitant 353 



Atomic ratios 



Copper 62. 50 per cent 62.50 H- 63.4 = 0.9S6 4.74 



Iron 11. 64 per cent 11.64 -i- 56 =0.208 1.00 



Sulphur 25.40 per cent 25.40-^32 =0.794 3.81 



99.54 



These results agree fairly well with the requirements of the 

 empirical formula Cu5FeS4. The relatively high proportion of 

 iron suggests the presence of a small quantity of chalcopyrite 

 which in preparing the sample for study had escaped detection. 



EXPERIMENT WITH SILVER SULPHATE SOLUTION 



The finely ground mineral (0.5926 gram) was digested first 

 on the steam bath for 6 hours and afterwards at room tempera- 

 ture. After 12 hours the solution was filtered from the insoluble 

 material. From the deposit were obtained 0.5983 gram of 

 free silver and 0.6037 gram of combined silver. Traces of copper 

 were present in the residue which also yielded 



0.0643 gram iron = 10.85 per cent of the mineral. 

 0.1478 gram sulphur = 24.94 per cent of the mineral. 



and from the solution were obtained 



0.3615 gram copper = 61.00 per cent of the mineral. 

 0.0053 gram iron = 0.89 per cent of the mineral. 



Atomic proportions of the copper dissolved by the silver 

 solution and the iron and sulphur recovered from the residue : 



Per cent 

 Copper 61 .00 



Iron 10.85 ^ 56.0 = 0.193 



Sulphur 24 .94 



and 



63.4 = 0.962 



32.0 = 0.780 



Cu Fe S 



0.962 : 0.193 : 0.780 = 4.98 : 1.0 : 4.04. 



The results obtained by this chemical reaction approximate 

 the requirements of the empirical formula, CusFeS^, more closely 

 than do the results obtained by a gross analysis of the sample. 



Atomic proportions of the dissolved copper and the precipitated 

 silver products: 



