444; Conversion of Bisulphuret of Copper into Sulphuret. 



These experiments appear to me sufficient to prove the 

 decomposition of the yellow ore. The loss of weight which 

 is detected is accurately made up by the peroxide of iron, the 

 sulphur of the sulphate of barytes and the copper. It may 

 appear to some that the alterations in weight in the last ex- 

 periment (4.) are trifling, but it must be remembered that 

 the copper pyrites was exposed, for a short time only, to a 

 weak current from a rather inconstant battery. If the action 

 had been continued longer, with a sustaining battery the loss 

 of weight would have been proportionally greater. 



5. With a view of ascertaining the effect of a more pow- 

 erful current on similar pieces of ore, I placed one piece in a 

 solution of the sulphate of copper, and another in water di- 

 vided from it by a membrane, connecting them respectively 

 with the positive and negative poles of a battery of twelve 

 pairs arranged as the couronne de tasses, excited with strong 

 brine. I thus procured a tolerably powerful, but constantly 

 weakening electric current. The arrangement was left for 

 two days, when the piece of ore in the solution of sulphate of 

 copper, which was connected with the negative pole, was 

 found to have crumbled down considerably, eight grains of 

 vitreous copper in a state of fine division having been col- 

 lected from the bottom of the vessel, the loss of weight on 

 the whole being ten grains and a half. Nothing is more in- 

 teresting than to observe, on the grand scale of natural ope- 

 rations, examples of processes which we have imitated in 

 the laboratory, and thus to find, at the same time, a proof of 

 the correctness of our experiments, and a complete elucida- 

 tion of a natural phenomenon. 



At the last annual meeting of the Polytechnic Society, a 

 communication was read from Joseph Carne, Esq., stating, 

 that at the mines in the neighbourhood of Marazion, the bisul- 

 phuret of copper was always found in the blue slate, whereas 

 the vitreous ore was constantly found in the red slate ; and 

 that the same fact was observed at the Cam Brea mines near 

 Redruth, where the yellow ore was invariably changed into 

 vitreous ore whenever the granite exhibited a red colour. 

 This tincture is due to the peroxide of iron ; and it is worthy 

 of remark, that the stain does not extend many feet on either 

 side of the load. 



I must be excused from remarking, that it appears to me 

 evident that the change of the bisulphuret of copper into the 

 sulphuret is explained in the preceding experiments, and 

 shown to depend upon the decomposing power of the electric 

 currents which circulate through the metalliferous veins, as 

 was discovered by Mr. Robert Fox, and the decomposing 



