PURPOSE: To enable any unexperienced person to simply measure an amount of available chlorine, by preliminarily adjusting the concn. of sodium thiosulfate so that the titration quantity thereof comes to a value showing the ratio of the amount of available chlorine.

CONSTITUTION: In the case of a conc. sodium hypochlorite solution (1% or more), about 1ml of said solution is accurately taken and diluted with a proper amount of water. Potassium iodide, hydrochloric acid and a starch solution are added to the diluted solution. Next, when titration is performed by a sodium thiosulfate solution (0.282N solution) prepared so as to be adjusted to 1ml with respect to 0.01g of available chlorine, titration quantity directly comes to an available chlorine amount. for example, if the titration quantity is 8.5ml, the amount of available chlorine in the sodium hypochlorite solution comes to 8.5w/v%. In the case of a dilute sodium hypochlorite solution, 10ml of said solution is accurately taken to perform the same treatment and titration is performed by the sodium thiosulfate solution (0.028N solution) and, by increasing the titration quantity 100 times, the obtained value directly comes to an amount of available chlorine.