[ ivi ] 



XXXV. On the Results of Mr, Fox's Expemnents on the Pro- 

 dudion of artificial Crystals by Voltaic Action, 



"11/^ E have alluded in page 83 of the last Number of this 

 ^^ Journal, in reference to a paper by M. Becquerel in 

 the Third Part of the " Scientific Memoirs," to the commu- 

 nications of Mr. Fox and Mr. Crosse at the Bristol meeting 

 of the British Association relative to the production of artifi- 

 cial crystals by voltaic action. We are now enabled, by the 

 kindness of Mr. Fox in sending specimens of the altered 

 ores for examination, to give a more exact account of the re- 

 sults of his experiments than we could otherwise have done. 



Mr. Fox's own statement is as follows : " The experiment 

 referred to was performed in the following manner : — An 

 earthenware trough was divided by a partition of moistened 

 clay into two cells, into one of which was put a piece of the 

 yellow sulphuret of copper, the cell being filled with a solution 

 of the sulphate of copper, and into the other a piece of zinc, 

 and the cell filled with water, either pure or slightly acidu- 

 lated by sulphuric acid. The zinc was then connected with 

 the copper ore by means of a copper wire passing over the 

 wall of clay. This simple voltaic arrangement soon rendered 

 the surface of the copper ore highly iridescent, then purple, 

 and in the course of a few days gray, the gray crust being 

 covered with metallic copper, deposited in brilliant crystals, 

 and with a slightly greenish soluble salt. This crust resembled 

 gray sulphuret of copper, and increased in thickness after the 

 operation had been continued several weeks." 



The crust on the specimens received from Mr. Fox was 

 thin, and the quantity so small that an exact analysis of it 

 could not be made. But the result of the examination to which 

 it was subjected approached so nearly to that of the Cornish 

 sulphuret as to warrant the conclusion of its being the same 

 chemical compound. The soluble salt was found to be a sul- 

 phate of copper and iron, which accounts for the iron that 

 the yellow copper ore had lost during its conversion into sul- 

 phuret. 



Mr. Fox considers that, assuming the gray crust to be sul- 

 phuret of copper, as it turns out to be, these results explain 

 why metallic copper occurs in our mines in contact with gray 

 and black copper ore, and not with the yellow sulphuret of 

 that metal ; and likewise why the former is generally found 

 nearer the surface than the latter, and also near cross courses 

 and in situations where it is most exposed to the action of 



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