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Owing to the limited contact period available a large dosage of chlorine is employed and the excess afterwards removed by the addition of a solution of sodium thiosulphate.

The amount of iodine liberated is therefore a measure of the copper in the solution, and when the sodium thiosulphate has been carefully standardized the method is extremely accurate.

The mixture is then cooled, acidified by means of sulphuric acid, and titrated with decinormal sodium thiosulphate solution.

Ores in which the copper is present as oxide or carbonate are soluble in sulphuric or hydrochloric acids, ferrous chloride, ferric sulphate, ammoniacal compounds and sodium thiosulphate.

Unfortunately, the term normal is sometimes given to solutions which are strictly decinormal; for example, iodine, sodium thiosulphate, &c.