Chlorimetry is the process of estimating the proportion of 'available chlorine' in Bleaching Powder (q.v.), which may vary from 20 to 40 per cent. The term available applies only to that portion of the chlorine which is easily liberated, and which takes part in the bleaching process.
Chlorine, which is present as chloride, as in chloride of calcium, , has no bleaching power, and is not estimated by chlorimetry.
The process is one of volumetric analysis, and the apparatus used is similar to that described in the article on Analysis (q.v.). There are several practical methods of chlorimetry, all based on the principle of measuring the oxidising power of the bleaching powder. This is arrived at by making a solution containing a definite amount of pure sulphate of iron, arsenious acid, or other substance capable of being oxidised, running in the solution of bleaching powder very slowly, and then by suitable tests determining the exact point when oxidation has taken place. By calculation the amount of 'available chlorine' is at once obtained. Where substances other than bleaching powder are under examination, slight modifications of the process may be necessary.