An example which was heated for 30 minutes required 20.5 c.c. of the barium chloride solution. This is equivalent to 20.6 per cent. of sulphur. The theoretical yield is 20.2 per cent.
Determination of Sulphur in Pyrites.—Take 1 gram of the finely-powdered sample, cover with 10 c.c. of nitric acid, and, when action has ceased, evaporate to a small bulk. Add 3 or 4 c.c. of hydrochloric acid, and again evaporate to a paste. Take up with 1 or 2 c.c. of dilute hydrochloric acid, dilute with water, transfer to a titrating-dish, add 10 grams of sodic acetate and 5 c.c. of acetic acid, and dilute with water to 500 c.c. Boil and titrate.
An example with 1 gram of a pure crystallized pyrites required 52.7 c.c. of the barium chloride solution, which is equivalent to 53.0 per cent. of sulphur. Theory requires 53.3 per cent. of sulphur.
Determination of Sulphur in Mispickel.—Take 1 gram of the powdered ore and evaporate with 10 c.c. of nitric acid, and take up with 3 or 4 c.c. of hydrochloric acid. If any globules of sulphur remain, again evaporate with nitric acid. Dilute, and transfer to the titrating-dish. Add 10 grams of sodic acetate, dilute with water, boil, and titrate. The mispickel carries (according to theory) exactly sufficient iron to precipitate the arsenic as ferric arsenate in an acetic acid solution, so no more iron need be added. The ferric arsenate will separate out as a yellowish-white flocculent precipitate.
An example required, in duplicate experiment, 18.5 c.c. and 18.7 c.c. of barium chloride, equivalent to 18.7 per cent. of sulphur. The formula, FeS2.FeAs2, requires 19.6 percent., but the sulphur generally varies considerably from this amount.
Determination of Sulphur in Burnt Ores.—Take 5 grams of the dried and powdered ore, and rub up with 4 grams of nitre; transfer to the platinum-dish; clean out the mortar with another gram of nitre, and add this as a cover. Heat, and extract with water as before; add the sodium acetate and acetic acid; and titrate. Burnt ores carry from 2.5 to 5 per cent. of sulphur. A series of four determinations gave:—
| "Baric Chloride" Required. | Percentage of Sulphur. | Gravimetric Results. |
| 12.6 c.c. | 2.52 % | 2.45 % |
| 29.9 " | 5.98 " | 5.84 " |
| 18.1 " | 3.62 " | 3.53 " |
| 22.0 " | 4.40 " | 4.43 " |
For ores carrying less than 1 per cent. of sulphur, take 10 grams for the assay.
Determination of Sulphuric Oxide (SO3) in Sulphates.—When the sulphur exists in the sample received by the assayer in an oxidised state as sulphate, it is usual to report it in terms of sulphuric oxide (SO3). In this case, the metal must also be reported as oxide. For example, an analysis of copper sulphate would be thus reported:—
| Oxide of copper (CuO) | 31.8 % |
| Sulphuric oxide (SO3) | 32.1 " |
| Water | 36.1 " |
| ——— | |
| 100.0 |