Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/470

Rh ON THB CONDITIONS OF MATTER.

457

iridescent After the action had been continued for some weeks, the following results were obtained : —

ITie piece of copper pyrites connected with the copper pole was changed over the entire surface into the gray sulphuret of copper. Of course this change was effected by the liberation of the sulphur and iron. The sulphur, at the moment of liberation, uniting with oxygen, is converted into sulphuric acid, which, combining with the barytes, forms the insoluble sulphate, of which 29 grains were collected, showing the presence of 10 grains of sulphuric acid, or the liberation of about four grains of sulphur, or the separation of nearly 10 grains of the sul- phuret of iron firom the ore. This iron was found partly in the solution, as muriate of iron, and partly as peroxide of iron, deposited over the un- changed piece of ore connected with the other pole of the battery.

Fig. 14.

60. Changes of this kind are constantly going on in nature, and we find numerous mines in which the progress of these decompositions can be traced. At Dolcoath copper mine, by some local action a portion of the lode, near a *' cross course," was converted into the gray sulphuret of copper; all other parts remaining in its original state of copper pyrites. Over the portion thus changed the prevalence of peroxide of iron was very marked. The same thing is observed in tiie Cam Brea mines, llie decomposition is not confined to the iron of the ore, but is continued to the destruction of the sulphuret of copper itself. I have detected in water flowing from the junction of the granite and day slate (Killas), at the 80 fiithom level in the Consolidated Mines, Grwennap, 1*25 grains of sulphate of copper in every 1000 grains of water.*

61. Whenever any changes of the kind described occur, it is evident that there must be a large quantity of electricity set in motion, in the form of a current Dr. Faraday has beautifidly shown ^^ that the elec-

see * Qeological Beport on Cornwall, Devon, and West Somerset,' by Sir Henry De la Beche. chapters x. zi. zU. p. 283-394.
 * For a description of the various eonditions of the metalliferons Teins of ComwalL

2 H

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