─────────────────┬──────┬─────────────────────┬─────────────────────── │ │ ASSAYS │ CONTENTS │ Cwt. ├────┬──────┬────┬────┼─────┬─────┬────┬────── │ │Pb% │Ag oz.│Zn% │ S% │ Pb │ Ag. │ Zn │ S │ │ │ │ │ │cwt. │ oz. │cwt.│cwt. ├──────┼────┼──────┼────┼────┼─────┼─────┼────┼────── Raw slime │128.1 │21.3│ 18.0 │16.8│13.1│27.28│115.3│26.2│16.78 Raw gypsum │ 54.9 │ │ │ │ │ │ │ │ 9.88 ├──────┤ │ │ │ ├─────┼─────┼────┼────── Total │183.0 │ │ │ │ │27.28│115.3│25.2│26.66 ──────────────────┼──────┼────┼──────┼────┼────┼─────┼─────┼────┼────── Sintered material│109.88│20.7│ 17.2 │ │4.80│22.74│ 94.5│ │ 5.27 Middling │ 14.47│17.7│ 15.7 │ │6.20│ 2.56│ 11.3│ │ 0.89 Fines │ 11.12│19.0│ 14.8 │ │7.50│ 2.11│ 8.2│ │ 0.83 ├──────┼────┼──────┼────┼────┼─────┼─────┼────┼────── Total │135.47│ │ │ │5.17│27.41│113.0│ │ 6.99 ─────────────────┴──────┴────┴──────┴────┴────┴─────┴─────┴────┴────── These results indicated practically no volatilization of lead and silver during the treatment, the lead showing a slight increase, viz., 0.47 per cent., and the silver 1.13 per cent. loss. A desulphurization of 70.4 per cent. was effected. A higher desulphurization could have been effected had this been desired. In the above tabulated results, the term “middling” is applied to the loose fritted lumps lying on the top of the charge: these are suitable for smelting, the fines being the only portion which has to be returned. In order to test the practicability of making sulphuric acid, a plant consisting of three large converters of capacity of five tons each, together with a lead chamber 100 ft. by 20 ft. by 20 ft., was then erected at Broken Hill, together with a dehydrating furnace, pug-mill, and granulator. These converters are shown in the accompanying engravings. A trial run was made with 108 tons of concentrate of the following composition: 54 per cent. lead; 1.9 per cent. iron; 0.9 per cent. manganese; 9.4 per cent. zinc; 14.6 per cent. sulphur; 19.2 per cent. insoluble residue, and 24 oz. silver per ton.