| Type of Cell. | Salt. | Power. | ||
| Per Pound of Available Chlorine. | ||||
| Pounds. | Per Cent Consumed. | Kilowatt Hours. | Efficiency Per Cent. | |
| Haas and Oettel | 10.7 | 15.4 | 3.8 | 31.9 |
| Kellner | 7.5 | 22.0 | 2.75 | 43.9 |
| Hermite | 11.2 | 14.5 | 2.87 | 42.2 |
| Mather and Platt | .... | .... | 2.75 | 43.9 |
| Dayton | 10.0 | 16.5 | 3.6 | 33.6 |
| Theoretical | 1.65 | 100.0 | 1.21 | 100.0 |
The cost of production depends upon local conditions: if alternating current is available at $30 per horse-power per annum, and low-grade salt can be obtained for $5 per ton the cost of 1 pound of chlorine would be
| Type of Cell. | Cost (Cents) Per Pound of Available Chlorine. | ||
| Salt. | Current. | Total. | |
| Haas and Oettel | 2.67 | 1.97 | 4.64 |
| Kellner | 1.87 | 1.43 | 3.30 |
| Hermite | 2.80 | 1.49 | 4.29 |
| Dayton | 2.50 | 1.92 | 4.42 |
The electrical and chemical efficiencies of the Haas and Oettel and Dayton cells, which contain carbon electrodes, are smaller than those containing platinum electrodes but for water sterilisation the carbon cells have been found to be more suitable. To prevent the action of magnesium salts on the platinum electrodes it is necessary to use a higher grade of salt or to provide means of purification. Because of the absence of a base and the presence of chlorides, electrolytic hypochlorite cannot be stored for more than a few hours without appreciable loss of titre. Unless used for the treatment of the effluent of a filter plant operated at a fairly constant rate a small storage tank is necessary to compensate for the irregular demand and to provide the head required by orifice feed boxes. Small variations can be made by regulating the flow through the cells but large ones are not compatible with efficiency, which is the highest under a constant load.
Claims have been made that electrolytic hypochlorite is more efficient as a germicide than bleach when compared on the basis of their available chlorine content but no evidence of it has been produced. Bleach contains an excess of base, which retards the germicidal action, and electrolytic hypochlorite contains an excess of sodium chloride, which accelerates it (Race[4]) but the ultimate effect is the same with both. This is shown in [Table XXIV].
TABLE XXIV.[A]—COMPARISON OF BLEACH
WITH ELECTROLYTIC HYPOCHLORITE
| Contact Period. | Bleach. | Electrolytic Hypochlorite. | ||
| Available Chlorine. Parts Per Million. | ||||
| 0.4 | 0.6 | 0.4 | 0.6 | |
| Nil | 182 | ... | ... | ... |
| 10 minutes | 130 | 10 | 120 | 8 |
| 1 hour | 66 | 1 | 60 | 0 |
| 2 hours | 3 | 0 | 1 | 0 |
| 31⁄2 hours | 0 | 0 | 0 | 0 |
| [A] Resultsare B. coli per 10 c.cms. | ||||
Electrolytic hypochlorite has a greater germicidal velocity than bleach but the difference is so small as to be of no practical importance. Rabs[5] experimented with various hypochlorites but was unable to find any appreciable differences in their germicidal action.
If electrical power can be obtained at a very low cost, or if the cost is merely nominal, as it is when there is an appreciable difference between the normal consumption and the peak load upon which the rate is based, the electrolytic hypochlorite method offers some advantages but in the great majority of plants it cannot economically compete with bleach. The instability of the liquor and cell troubles have also prevented the process being generally utilised. Baltimore and Cincinnati experimented with this method but did not adopt it. Winslow[6] has reported that, owing to the difficulty in obtaining bleach since the outbreak of war, Petrograd has used electrolytic hypochlorite made from salt.
Diaphragm Process. The various types of diaphragm cells that have been commercially operated are of two varieties: (1) cells with submerged diaphragms and (2) cells in which the electrolyte comes in contact with one face only of an unsubmerged diaphragm.