Subsequent to the introduction of the Huntington-Heberlein process in Australia, Messrs. Carmichael and Bradford, two employees of the Broken Hill Proprietary Company, patented a process which bears their name. Instead of starting with lime, or limestone and galena, as in the Huntington-Heberlein process, they discovered that if sulphate of lime is mixed with galena and the temperature raised, on blowing a current of air through the mixture the temperature rises and the mass is desulphurized. The process would thus appear to be a corollary of the original one, and the reactions in the converter are identical. Owing to the success of the acid processes in separating zinc sulphide from the tailing at Broken Hill, it became necessary to manufacture sulphuric acid locally in large quantity. The Carmichael-Bradford process has been started for the purpose of generating the sulphur dioxide necessary, and is of much interest as showing how gases rich enough in SO₂ may be produced from a mixture containing only from 13 to 16 per cent. sulphur. Gypsum is obtained in a friable state within about five miles from Broken Hill. This is dehydrated, the CaSO, 2H₂O being converted into CaSO₄ on heating to about 200 deg. C. The powdered residue is mixed with slime produced in the milling operations and concentrate in the proportion of slime 3 parts, concentrate 1 part, and lime sulphate 1 part. The proportions may vary to some extent, but the sulphur contents run from 13 to 16 or 17 per cent. The average composition of the ingredients is as given in the table on the next page. These materials are moistened with water and well mixed by passing them through a pug-mill. The small amount of water used serves to set the product, the lime sulphate partly becoming plaster of paris, 2CaSO, H₂O. While still moist the mixture is broken into pieces not exceeding two inches in diameter and spread out on a drying floor, where excess of moisture is evaporated by the conjoint action of sun and wind. ─────────────────┬─────┬───────────┬────────┬──────── │SLIME│CONCENTRATE│CALCIUM │AVERAGE │ │ │SULPHATE│ ──────────────────┼─────┼───────────┼────────┼──────── Galena │ 24 │ 70 │ │ 29 Blende │ 30 │ 15 │ │ 21 Pyrite │ 3 │ │ │ 2 Ferric oxide │ 4 │ │ │ 2.5 Ferrous oxide │ 1 │ │ │ 1 Manganous oxide │ 6.5│ │ │ 5 Alumina │ 5.5│ │ │ 3 Lime │ 3.5│ │ 41 │ 10 Silica │ 23 │ │ │ 14 Sulphur trioxide │ │ │ 59 │ 12 ─────────────────┴─────┴───────────┴────────┴────────