Lieutenant Nesfield of the Indian Medical Service is said to have used liquid chlorine ps as a disinfectant of water in 1903. Siiice 1910 ramified chlorine gas has been used in 'corral cantonments of the United States army sad at Wihnington. Philadelphia, Brooklyn, New York and to many other places. On the Western ROM during the Great World War it was successfully applied by means of liquid chlorine machines. The Dunwoodic chlorin ating plant for New York City has a daily capacity of 400,000.000 gallons. The chlorine gas is introduced into the water in the aqueduct as it leaves the Kensico reservoir to ensure practical sterilization of the water before it reaches the city of New York This process has some advantages over the hypochlorite or ozone process, though there is danger of injury to operators from leakages of the gas, which is injurious to the lungs and deadly ii inhaled in concentrations of .06 per cent. The rela tive efficiency and cost of installation of these several processes are usually considered be fore any one is installed. Recently halazonc (CLN•O,S has been found to be an efficient chemical for sterilizing heavily polluted waters.
6. The Application of (a) Ozone, or (b) Ultra Violet Rays of Light.—(a) 'Ozone is produced,' says Allen Hazen in his 'Clean Water and How to Get It,' p. 101, 'by the discharge of high-tension electricity through air under certain conditions. The air is afterward pumped through the water to be treated or otherwise the water is showered downward through towers in which the ozonized air is circulated.° Ozone, being a modification of oxygen, is a more active oxidizing agent than oxygen and is a powerful disinfectant. There are many devices for the application of ozoned air to the purification of water, but the process is equally efficient but more expensive than the application of the chemicals hereinbefore de scribed. The De Frise system at Saint Maur gives satisfaction in sterilizing the Marne water after sedimentation and filtration. Sanitary commissions, health authorities and specialists have extensively experimented with it in Europe and found ozonized air, when properly applied, was destructive of bacteria in water. The application of the ozonized air produced by the ozonizers, of which there are several in use, such as the large plant of 128 Siemens and Halske ozonizers at Petrograd, with five sterilizing towers, is as follows: The ozonized air enters the bottom of water towers and is absorbed by the water as it de scends through the layers of gravel in some and sieves in other towers after the water has first passed through sedimentation and pre liminary sand-filter basins. Such water as it enters the sterilizer may still contain several hundred bacteria per cubic centimeter. The pathogenic bacteria, such as typhoid and cholera microbes, are destroyed by ozonized air, though the more hardy and harmless ones may escape destruction. In the higher towers, the steriliz
ing ozonized air is injected at several levels, as at Ginnekin. Holland. where all pathogenic bacteria are destroyed. The process is more costly than the hypochlorite process, hut it has been pronounced by an English expert as 'ideal.' It is in use in Brussels. Ginnekin Paris, London, Berlin, Petrograd, Florence, Chartres, Nice, Saint Maur, Wiesbaden, Paderborn and in -:any other European cities, and at one plant in Philadelphia and in Ann Arbor, Herring Run. Md , and a few other places, but it is not at present extensively used in Amenca. It has some advantages over the chlorine processes. The Otto process in use in Nice purifies 5,000,000 gallons daily. Its general use in Europe, after most thorough tests as to its efficiency, may result in its more general use in America.
(b) Ultra-violet rays of light. One of the recently discovered processes for the destruc tion of pathogenic bacteria is the application of ultra-violet light to the flow of water through flumes, so that the organisms are exposed to the concentration of its rays. Several ultra violet ray sterilizers have been devised and suc cessfully used in the rapid destruction of bacteria. It was demonstrated, by experiments made by Henri Helbronner and others at Sorbonne University in Paris, that bacteria can not long endure the direct ultra-violet rays of three ten-thousandths of a millimeter in length. American tests have shown that it required only one-twentieth of a second to kill bacteria with such rays, but they must not be inter cepted by suspended organic matter in the water. It is, therefore, necessary that the water be rid of turbidity before applying the ultra violet ray process to its sterilization, for Dr. Von Reckling-Hausen declared that it is the light and not chemical reaction that produces the germicidal results. Ultra-violet ray tests made at Luneville, France, on water containing 60,000 germs per cubic centimeter reduced the number to 10 germs per cubic centimeter and destroyed all B. toll, The death rate of 70 to 160 of typhoid fever also became negligible. Since devastations of the Great World War began, the water supply of northern France has been contaminated at the rate of 4,600 putrescent bacteria and 1,000 B. coli per cubic centimeter and they may go on for years in an increasing ratio, in consequence of the count less burials and pollution of the underground waters of the war zone. The Quartz-Mercury lamp is sometimes used to produce ultra-violet rays:for the sterilization of water. That process eliminated nearly all the bacteria from the raw Durance river water at Marseilles.