The substitution of a sodium hypochlorite solution for the ordinary calcium hypochlorite solution obtained from common bleaching powder has been the aim of specialists for many years. As early as 1851 a patent was taken out by Charles Watt for decomposing chlorides of the alkali metals and the formation of hypochlorites. It was not until 1886 that a practical method was devised for producing an electrolysed solution of salt, but in that year Hermite introduced a continuous process in which an electrolysed solution having a strength of three grammes chlorine per litre was passed continuously into the potcher. Many patents for the electrolysis of salt have been taken out during the last twenty years, of which the Bird-Hargreave process is in operation in England, the Rhodin process in America, the Siemens and Halske in Norway, and the Oettel and Haas apparatus in Germany. The figures relating to the latter apparatus may be mentioned as typical of the present condition of electrolytic bleaching. The apparatus consists of a narrow rectangular trough divided into a number of chambers through which a solution of brine flows at a constant and steady rate. The electric current is passed through the solution by suitable electrodes, the temperature being kept down by means of a cooling coil. The cost of producing the bleach liquor as given by the inventors of the apparatus from the results of actual working are shown in the following table:-- TABLE GIVING ANALYSIS OF COST FOR PRODUCING BLEACH LIQUOR. Capacity of tank 750 litres = 166 gallons. Strength or density of brine 1·5 Baumé, or 23 Twaddell. 286 lbs. of common salt required for 166 gallons.