The Le Sueur, Gibbs, Crocker, Billiter-Siemens, Nelson, and Hargreaves-Bird cells are of the submerged diaphragm variety. The Nelson cell has been operated for some time at the filtration plant at Little Falls, N. J. The cells are fed with brine solution previously purified by the addition of soda ash and have given fairly successful results although the cost of maintenance is comparatively high. Tolman[7] has reported that several towns in West Virginia use a bleach solution prepared by absorbing chlorine, manufactured by the Hargreaves-Bird process, in lime water; the solution contains about 1.95 per cent of available chlorine.
The diaphragms in both the submerged and unsubmerged types are usually constructed either with asbestos paper or cloth, placed in such a manner as to divide the cells into two separate compartments: the anodic, into which the brine is fed and where the chlorine is produced; and the cathodic, where caustic soda is formed.
By maintaining the liquor in the anodic compartment at a higher elevation than in the cathodic one, the direction of flow is towards the latter, but owing to osmosis and diffusion the separation is not complete and a portion of the caustic soda passes the diaphragm and produces hypochlorite with a consequent loss of efficiency and rapid deterioration of the anodes. With the exception of the Billiter-Siemens cell, the submerged diaphragm cells operate at not more than 85 per cent efficiency and the cost of maintenance is usually high.
In the non-submerged diaphragm types the invasion of the anodic compartment by caustic is much reduced and the efficiency and life increased.
An electrolyser of the non-submerged diaphragm type is the Allen-Moore cell which has been adopted by the Montreal Water and Power Co. This has been described by Pitcher and Meadows.[8] The general lay-out of the installation is shown in [Fig. 10], and the essential features are: a salt storage bin having a capacity of 40 tons; the brine saturating and purifying apparatus; duplicate 15 horse-power motor-generator sets; four chlorine cells; and the silver ejectors and distributing lines for carrying the chlorine solution to the point of application.
Fig. 10—Brine Saturating and Purifying Equipment.
The brine solution, which is prepared by passing water through the saturators previously filled with salt, is delivered to the two concrete reaction tanks where an amount of soda ash and caustic liquor sufficient to combine with the calcium and magnesium salts is added, and the mixture filtered through sand and stored in the purified brine tanks. To prevent the formation of hypochlorites by the interaction of chlorine and alkali, the alkalinity of the liquor is determined and sufficient hydrochloric acid added to ensure an acidity of 0.01 per cent. The acid brine is delivered at one end of the four cells ([Fig. 11]) each of which is 7 feet long and 203⁄8 inches wide and consumes 600 amperes at 3.3 volts. The cell box is built of concrete and is provided with a perforated wrought iron cathode box and graphite anode plates which are separated by an unsubmerged asbestos paper diaphragm.