7. By Sterilization.— Purification h also gen erally effected by sterilization, which is used in conjunction with several of the processes al ready mentioned. By reason of the various chemicals used and their germicidal action on micro-organisms, irrespective of the other aLencies employed, too much attention cannot be given to the process of sterilization.
In recent years some public water supplies have been purified by sterilization, where sewage bacteria now known as °aerobic spore forming bacilli, including B. erogenes capsul a1u4, B. cnteruidis, or B. sporogenes and B. streptucocci were present. Active agents were necessary to destroy them. The basins or reser voirs where the process of sterilization is in operation must be cleansed two or more times a day.
In 1892, the English employed calcium hypo chlorite to disinfect sewage. In the following year the American Public Health Association recommended its use as a disinfectant. It was known in 1892 that hypochloritcs were efficient water sterilizers. In 18'97 they were first used at Maidstone. England. to purify its water sup ply, after a typhoid epidemic. In 1904 they were applied to disinfect the water pipes in London. Thereafter they came into quite gen eral use in this and other countries. Hypo chlorite of lime and hypochlorite of soda are the principal chemicals used. Where hypo. chlorite of lime is used its solutions are thoroughly mixed with the raw water in the proportion of 5 to 10 pounds of the powder to 1,000,000 gallons of water, which is destruc tive of such pathogenic germs as typhoid, cholera and other bacilli. The objection to this chemical is that a sludge is formed, which interrupts the flow through the orifices and is also injurious to aquatic life, when deposited is fresh waters. Hypodilorhe of soda, elec trolytically produced, is somewhat more de structive of pathogenic bacteria than hype chlorite of lime. It is not difficult to and does not form sludge. The 'tes, however, are not a substitute for Itration, but rather additional agencies, that may be used to ensure complete destruction of pathogenic germs. Some spore-forming bacteria it water are not pathogenic and not all of these are destroyed, because they are hardy and not af fected by any of these chemicals, when in such small proportions as not to affect the water deleteriously, but made sufficiently active to destroy pathogenic germs, which are less hardy.
Many cities in this and in other countries use the hypochlorite processes in connection with sedimentation and filtration.
Francis F. Langley reported (American Journal Public Health, 4 Dec. 1914) that two billion gallons of water per day were being treated with bleaching powder, or chlorine gas As already stated, liquid chlorine being the liquification of chlorine gas, produced by the electrolysis of sodium chloride in the mamifae tore of caustic soda, is also used to sterilize water supplies. There are several devices for applying the gas, which is eliminated from the liquid by heat, to the tanks of water to be treated. The gaseous vapor is diffused through the water and destroys the pathogenic germs. Some of the chlorinated water so sterilized in the tower of Wilmington contained only from 6 to SO bacteria per cubic centimeter. Liquid chlorine is one of the sterilizing agencies used in Chicago Stock Yards, at Philadelphia, Pa., Saint Louis, Mo., Trenton and Newark, N. J., Cincinnati, Ohio, Niagara Falls and Ossining, N. Y., Hartford and Stamford. Conn., Saint Catherines and other places in Canada and at Honolulu, Hawaii, and elsewhere.
The ferrochlorine process of sterilization has been tested in Paris and found to be an effi cient bactericide, though on account of its cost it is not in general use. Another sterilizing chemical was proposed in the form of copper sulphates, but that has not been generally adopted. It was proposed as a sterilizing process to dispose of microscopic organisms. The research work of the Bureau of Plant Industry of the United States Department of Agriculture D. D. Jackson in his work on 'Odors and Tastes of Surface Waters,' and especially George C. Whipple. department awi neer under the Burr-Henna-Freeman Commis sion, on the Additional Water Supply of New York City, and others have called attention to aloe, and diatomacee (dienonsz), or now classified as vegetative or ganisms, varying in diameter from one thou sandth of a millimeter to one millimeter. Several species of these microscopic organ isms are found in fresh waters. Several species • .1,84,14e:es have been localized in the waters : Alahama, South Carolina and North Caro na by Dr. H. R. Carter and others of the Crated States Public Health Service. Anopheles are the cause of malaria. Mosquito-eating fish are being introduced to rid such waters of the Anopheles larvae.