Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/469

456 458 INFLUENCE OF VOLTAIC ELECT&ICITT

same lodes, divided by a fissure or cross course. In East Pool mine I succeeded in obtaining the decompodtion of iodide of potassium by the current drcnlating through the wires ; but Mr. Fox has since then suc- ceeded in forming at Pennance Mine, near Falmouth, an electrotype in copper, from the current circulating through two wires connected with two disfflimilar lodes, which were brought to the surface and dipped into a vessel contiuning sulphate of copper.*

57. That these currents are not due to any chemical action exdted at the points of contact between the conducting wires and the ore of the lodes, is proved by the £act, that whether plates of platina, or of copper^ or of zinc, were employed in making contact, the current obseryed a constant direction. That die electricity may not be due to chemical decomposition going on within the lode itself is less satis&ctorily made out

That the ordinary sulphurets of copper in Cornwall are exceedingly liable to decomposition may be readily proved by the following simple experiments.

58. If we put into a cylindrical vessel a solution of sulphate of copper, and float upon it a weak solution of any alkaline salt, and Uien

P£g^ l^ suspend a piece of yellow copper pyrites (a double

sulphuret of copper and ironf), so that one portion is in die metallic solution (i), and the other in tbe alka- line solution (a)f in a very short time a change of colour will be observed over tihat part of the ore in the copper solution, but not over any other part After a few days, the change still going on, a deposit of peroxide of iron will be found around the vessd, at the surface of the denser fluid. The following form of the experiment will show that tins is set free from the part under- going decomposition.

59. Two pieces of copper pyrites being connected with a constant voltaic battery of Daniell, were placed in a solution of the muriate of barytes (Fig. 14). Within a few hours sulphate of barytes was predpi- tated, and the ore connected with the copper pole became beautifiilly

t Specific graTity •*« «•*••••• 4*3 Copper* •«•••••. 30*00 Iron ••••*•••. 32*80
 * See Bepoiti of the Royal Cornwall Polytechnic Society for the yean 1842, 3, 4>

Sulphur * «. 35*16

Earthy matter 0*00

AnenieandloM * 2' 14

Analyili of a cryttalUsed specimen hy Mr. Richard Phillips of the Mweum of EoongmJe Oeology, giTen inPhilipa'a * Mineralogy/

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