In-situ production of sodium hypochlorite is one of the oldest electrochemical processes of the chemical industry. During the past twenty years a new "in-situ" hypochlorite industry has developed. Construction and performance of present-day cells are considered in detail. Modern cells are fed with seawater or similar weak brines and yield solutions suitable for disinfection, e. g. in breweries, laundries, etc., or for treatment of municipal sewage. Particular importance attaches to units for chlorination of cooling water for power stations or on board ships, thus hindering growth of organisms leading to operating failures. The article closes by considering development trends.Aqueous solut,ions of sodium hypochlorit,e were formerly manufactured by electrolysis of strong brine solutions, and were largely used in bhe paper, textile, and chemical or pharmaceutical industries. With the subsequent expansion of the chlor-alkali industry, however, alternative production routes were found increasingly economic, e.g. mixing of thr gaseous chlorine and NaOH formed in chlorinc cells and scrubbing of the ,,tail-gas" chlorine with sodium hydroxide in packed towers. Thus the original process became uncompetit,ive and only one such plant is now Idieved t o be still operating (in the Basle area). Meanwhile, however, a new and very vigorous industry has come into being selling equipment for ,,in-situ" manufacture of sodium hypochlorite for a wide variety of applications. Most of these applications are based on the strong disinfectant properties of sodium hypochlorite, which w(' shall now consider.
Disinfectant and Other Properties of Sodium HypochloriteDilute aqueous sodium hypochlorite is not only an excellent disinfectant, but has ot'her useful properties such as that of repression of marine growths and fouling [l -31. Sodium hypochlorite may be commercially purchased. However it is always dilute and its storage therefore involves large volumes of liquor which, in any case, deteriorate with time. A half-life of 100 clays has been quoted. Its chief competitor, liquefied chlorine, can be purchased fairly cheaply when quantities are large and shipping distances are not too great. Equipment is also available for continuous injection of chlorine [4]. However, operators are increasingly apprehensive of the dangers, both natural and those due to anti-social elements, latent when large amounts of this gas are stored.A potential solution to the chlorine supply problem, design and erection of miniature chlor-alkali mercury cells, was thwarted by high labour costs and the economic disadvantages of small scale operation. Furthermore, such plant,s require a source of saturated brine. In contrast, thc on-site dectrolysis of sea-water in a simple undivided cell afforded a safc and reliable source of hypochlorite solutions, and the idea of such a process ensuring continuous availability of disinfectant without depeiidance on outside suppliers needs no apology.
Applications of the MethodThe revival of electrolytic hypochlorite nianufacture began...
