Where very cheap electrical power can be obtained, the cost per pound of available chlorine is less for the electrolytic method just described than for liquid chlorine or chlorine obtained from bleach; but this condition obtains in very few places. Mr. J. A. Meadows has suggested to the author that the cost could be reduced by converting the chlorine gas into hypochlorite and then adding dilute ammonia as in the chloramine process (_vide_ page 115). The caustic liquor, usually run to waste from the cathodic compartment, could be delivered into a feed box from which it would be drawn off by the water injector used for dissolving the chlorine gas. BIBLIOGRAPHY [1] Lunge and Landolt. Jour. Soc. Dyers and Colourists, Nov. 25, 1885. [2] Kershaw. Jour. Soc. Chem. Ind., 1912, =31=, 54. [3] Rickard. Quar. Bull. Ohio Board of Health, Oct.-Dec., 1904. [4] Race. Jour. Amer. Waterworks Assoc., 1918, =5=, 63. [5] Rabs. Hygienische Rundschau, 1901, 11. [6] Winslow. Public Health Rpts. U. S. P. H. S., 1917, =32=, 2202. [7] Tolman. Jour. Amer. Waterworks Assoc., 1917, =4=, 337. [8] Pitcher and Meadows. Jour. Amer. Waterworks Assoc., 1917, =4=, 337. CHAPTER IX CHLORAMINE Chloramine (NH_{2}Cl), a chemical compound in which one of the hydrogen atoms of ammonia has been replaced by chlorine, was discovered by Raschig[1] in 1907. Chloramine was prepared by cooling dilute solutions of bleach and ammonia and adding the latter to the former contained in a flask surrounded by a freezing mixture. The proportions were as the equivalent weights of anhydrous ammonia and available chlorine (approximately two parts by weight of chlorine to one part by weight of ammonia). After gas evolution had ceased the mixture was saturated with zinc chloride and the magma distilled under reduced pressure. The distillate was a dilute solution of comparatively pure chloramine. The first to notice the effect of ammonia on the germicidal value of hypochlorites was S. Rideal[2] who noted that during the chlorination of sewage, the first rapid consumption of chlorine was succeeded by a slower action which continued for days in some instances, and was accompanied by a germicidal action after free chlorine or hypochlorite had disappeared. Rideal stated that: "It became evident that chlorine, in supplement to its oxidising action, which had been exhausted, was acting by substitution for hydrogen in ammonia and organic compounds, yielding products more or less germicidal." On investigating the effect of ammonia on hypochlorite it was found that the addition of an equivalent of ammonia to electrolytic hypochlorite increased the carbolic acid coefficient of 2.18, for one per cent available chlorine, to 6.36 (nearly three times the value). Further experimental work showed that the increase was due to the formation of chloramine.