SOMETIME since Mr. J. V. Parkes, the Inspector of Mines, asked me for some information as to the interference caused by copper ores in the MacArthur-Forrest process of extracting gold. On consulting the text books but little could be found bearing on this subject, and this having been cited in some recent articles by Messrs. Butters and J. E. Clennell on "The Chemistry of the Cyanide Process" in the Engineering and Mining Journal, 54, 1892, 391-417, it is not necessary for me to recapitulate it here.In the absence of a full library of chemical literature, it was impossible to make such a complete search as was desirable before starting work, and this must be my excuse for bringing forward some matter which may not be entirely new.Messrs. Butters and Clennell, in the articles above quoted, have gone very thoroughly into the losses involved in the cyanide process for extracting gold, and indicated with what classes of ore it may be profitably used, but they have left untouched some points on which I had been experimenting some time before their papers were seen here, and which also bear more or less on this process.