Mr. Skey also showed by very carefully conducted experiments that the metallic sulphides are not only better conductors of electricity than has hitherto been supposed, but that when paired they were capable of exhibiting strong electro-motive power. Thus, if galena and zinc blende in acid solutions be connected in the usual manner by a voltaic pair, sulphuretted hydrogen is evolved from the surface of the former, and a current generated which is sufficient to reduce gold, silver or copper from their solutions in coherent electro-plate films. The attributing of this property of generating voltaic currents, hitherto supposed to be almost peculiar to metals, to the common sulphides found in metalliferous veins, led Mr. Skey to speculate how far the currents discovered to exist in such veins by Mr. E. F. Fox might be produced by the gradual oxidation of mixed sulphides, and his conclusion is that veins containing bands of different metallic sulphides, bounded by continuing walls, and saturated with mineral waters, may constitute under some circumstances a large voltaic battery competent to produce electro-deposition of metals, and that the order of the deposit of these mineral lodes will be found to bear a definite relation to the order in which the sulphides rank in the table of their electro-motive power. These researches may lead to some clearer comprehension of the law which regulates the distribution of auriferous veins, and may explain why in some cases the metal should be nearly pure, while in others it is so largely alloyed with silver. The following extract was lately clipped from a mining paper. If true, the experiment is interesting:-- “An American scientist has just concluded a very interesting and suggestive experiment. He took a crushed sample of rich ore from Cripple Creek, which carried 1,100 ozs. of gold per ton, and digested it in a very weak solution of sodium chloride and sulphate of iron, making the solution correspond as near as practicable to the waters found in Nature. The ore was kept in a place having a temperature little less than boiling water for six weeks, when all the gold was dissolved, except what would be equal to one ounce per ton. A few small crystals of pyrite were then placed in the bottle of solution, and the gold began immediately to precipitate on them. It was noticeable, however, that the pyrite crystals which were free from zinc, galena, or other extraneous matter received no gold precipitate. Those which had such foreign associations were beautifully covered with fine gold crystals.” Experimenting in a somewhat similar direction about eight years ago, I found that the West Australian mine water, mentioned on page 85, with the addition of an acid, was a solvent of gold. The idea of boiling it did not occur to me, as the action was fairly rapid in cold water.