Mexican Paper - The Cyanide-Assay for Copper (Discussion, 1027)

In spite of its recognized irregularities, the cyanide-assay for copper has always been popular among volumetric methods, being easy and rapid, and reasonably accurate when the solution tested contains nothing but pure copper and ammonium salts. In order to secure this condition, however, especially in operati~ig on low-grade ores, tailings and slags of complex composition, it is the practice to precipitate the copper from the ore-solution,—usually by means of metallic zinc or aluminum. The copper thus precipitated in the metallic form must be dissolved again; and the separa tion is never, in practice, complete, since an appreciable amount of the copper remains behind in the first solution, and the second solution always contains some of the other metals of the gangue; so that the result is at best but partially satisfactory. On the other hand, if this course is not pursued, but (as is