──────────────────────────────┴─────────┴────────┴────────┴─────── ──────────────────────────────┬────────┬────────┬────────┬─────── │ Nickel │ Tin │ Oxygen │ Sulphur ──────────────────────────────┼────────┼────────┼────────┼─────── 1. Electrolytic conductivity │ 0·006 │ .. │ 0·008 │ nil copper, │ │ │ │ 2. Lake copper, │ 0·0146 │ nil │ 0·070 │ .. 3. Best select copper, │ 0·061 │ .. │ 0·143 │ .. 4. Tough pitch copper, │ 0·060 │ .. │ 0·120 │ .. │ .. │ .. │ 0·284 │ .. 5. Copper fire-box plate (ran │ │ │ │ 500,000 miles, Met. Ry.),│ 0·3039 │ .. │ 0·0181 │ 0·0064 │ │ │ │ INTERMEDIATE PRODUCTS— │ │ │ │ Refined converter copper, │ .. │ .. │ 0·284 │ .. │ .. │ .. │ 0·12 │ 0·01 Cathode copper, │ .. │ .. │ 0·005 │ .. Black copper, │ 2·04 │ 0·07 │ .. │ 0·80 │ .. │ .. │ .. │ 0·796 Cement copper (Spanish), │ .. │ .. │16·00 │ 5·10 │ .. │ .. │ .. │ 0·48 Blister copper, │ 0·0–0·2│ 0·0–0·5│ .. │ 0·112 Chili bar, │ .. │ .. │ .. │ 0·909 ──────────────────────────────┴────────┴────────┴────────┴─────── (2) Sulphide ores supply the bulk of the world’s copper, constituting upwards of 80 per cent. of the total. (3) The oxidised ores are found in most copper districts, though usually to only a limited extent. They are often gossan deposits produced by weathering or by decomposition of sulphides, hence are generally found nearer the surface, changing to sulphide with depth. The supply of copper from oxidised ores, which was at one time very large, is decreasing rapidly, and the greater proportion of the copper now obtained from them comes from the more recently developed deposits, of which those at Tanganyika afford an example. More than 200 minerals which contain copper are known, but most of them are unimportant from the smelting point of view. The characteristics of the more noteworthy may be fully studied from text-books of economic mineralogy.