PURPOSE: To increase the size of an NaCl crystal, and to suppress a perchlorinating reaction by supplying simultaneously excess NaOH and chlorine into an aq. soln. of NaOCl, and reducing the NaOH concn. when the supply of the former is stopped in the titled manufacture by the reaction of chlorine with NaOH.

CONSTITUTION: About 40W60wt% aq. soln. of NaOH and chlorine are simultaneously supplied into an aq. soln. of NaOCl having a concn. wherein NaCl is not deposited, and the supply velocity is regulated to ≥1.2 equivalent ratio of NaOH to chlorine to carry out the reaction. And when the NaOH concn. in the reaction liquid is reduced to 7W17wt%, only the supply of NaOH is stopped and the supply of chlorine is continued to continue the reaction until the remaining NaOH is substantially eliminated. The NaCl crystal can be grown as large as possible in this way, and the perchlorinating reaction can be suppressed at the same time.