Professor Burci, of the Institute of Superior Studies at Florence, director of the iron and copper mines at Traversella, in Piedmont, and one of the most distinguished geologists and mining engineers of Italy, has just published a highly interesting account of the mines above alluded to, containing a description of a new process for separating copper ore from iron ore, invented by M. Sella, an engineer well known to the scientific world by his " Studies on the Mineralogy of Sardinia." In the mines of Traversella, the horizontal development of their galleries measures 47 English miles, and they belong to different proprietorc, one of whomCher. Riccardi di Netroremarking that the iron ore obtained was intermingled with a considerable proportion of copper pyrites, requested M. Sella, in 1854, to examine whether copper might not be extracted as well as iron. After much attention to the subject, M. Sella declared that the copper pyrites were much too thinly disseminated among the magnetite, or magnetic iron ore, to be profitably separated by the common process of picking ; that the specific gravity of the two ores was so nearly alike, that they could hardly be separated by washing. At length, however, M. Sella hit upon a plan which has been crowned with complete success. We have several times had occasion to describe electro-magnetic machines, the great principle of which consists in this: that a bar of soft iron can be temporarily magnetised by an electric current, and be made to lose its magnetic power instantly by the cessation of the current. M. Sella had recourse to this principle, and invented an apparatus, consisting of a wheel provided with fifty-four electro-magnets, which being turned over the ore, previously triturated by stampers, attract, when magnetised, all the magnetite which they let fall elsewhere on losing their magnetism. By this highly ingenious method all the copper pyrites, which, of course, cannot be attracted, is duly separated, at a very small cost, from the iron ore, among which it was previously as good as lost.London Engineer. [Such a machine was in operation in America twelve years ago, and was illustrated and described on page 305, Vol. III. (old series), of the SCIENTIFIC AMERICAN. Theoretically, the machine was constructed upon correct principles to effect objects similar to those set forth in the foregoing extract, but we understand it was used only for a very short period. In our opinion, it might be usefully applied in various mines.
This article was originally published with the title "Picking Ore by Electro-Magnetism"