In all these matters conditions differ and it is necessary to specialise in the treatment of each municipal water supply. No two are identical, unless they form parts of the same system, as now does the supply for several boroughs of New York City, when the same general principles may apply, as to the colter. non, purification and distribution of water for such horentichs But in most cases, each supply must he studied independently of all others and provided for, with special reference to its peculiar characteristics, whiCh are as variable as earth's watersheds Removal of the Salts of Calcium, Magne sium, Iron and Manganese.— In some well and other ground waters such minerals as salts of calcium, magnesium, iron and manganese are found in solution. An ar tificial zeolite. known as •Permutit," was pro duced by Dr. Richard Gans and is used to rid water of its calcium and magnesium. Caustic soda, the silica of sodium, barium carbonate and other chemicals are also used for that pur pose. The Reiser* zeolite and other water softeners are in use in this and other coun tries. C. P. Hoover and R. D. Scott in Ohio, R. N. Kimmard, Dr. Edward Bartow, Samuel A. Greeley, Francis G. Wickware and others have written on the subject of water softening by the •Permutit" or other processes. There is a large plant for softening at Winnepeg. Canada, and smaller ones at Oberlin, Ohio, and elsewhere in the United States.
The extraction of iron and manganese has also been studied by Dr. Gans, M. S. Apple baum, Dr. H. Luhng, Frank E Hale, R. S. Weston, F. C. Amsbary and others. Plants for deferrization of water have been installed at Middleboro, Mass., at Rotterdam, at Dresden, Breslau and Hamburg in Germany and else where. The process is described in the reports of those specialists and is generally effective in eliminating those minerals from such waters, though there may remain in water pipes the crenothris, and gallionella organisms that flourish in such solutions. Karl Kraepelin found 60 species of animalcula, infesting the water pipes of Ham burg and known as •pipe moss comprising sponges, spongilla listviatilis and lacurins, tow hum, snails, lice,' menus aquaria's, 'water crabs' (Gammon": pales) and other species. Rotterdam, Boston and Brooklyn have
encountered troublesome growths in thew water pipes.
Minor Processes.— Some of the minor processes of purification involve the use of the small mechanical filters, consisting of small basins of layers of sand, over which gelatinous films of aluminum hydrate are founol. Water passes through these rapidly and the bacteria are caught in gelatinous material and removed. Such filters are used to clarify muddy waters during freshets and in limited areas, where suffi cient land cannot be economically obtained for sedimentary and the slow sand filter beds. There are several hundred in use in America. Where properly constructed and operated, satis factory results are obtained, but they must be darned twice or more times a day and the chemicals used in sterilization are expensive. Several such filters, including the Candy and Reiser* types, are in successful operation.
The Lawrence filter first installed in the United States was the forerunner of other mechanical filters, that have proved quite effi cient in purifying municipal water supplies.
Porcelain Filters.— Prof. Louis Pasteur and others have suggested porcelain and baked infusorial earth, as additional safeguards, but the necessity of their frequent sterilization and the cost of such filters render them im practicable for general water-supply purposes. Bacteriologists now contend that microbes are propagated in and are not eliminated by porce lain filters. There are other minor processes for the purification of water, such as granular bed filters, charcoal filters, porous wall filters Berke fell system, Maignen method and the boiling of water. None of these processes are efficient in disposing of all the pathogenic bacteria. Some of these, such as B. andseneis and its spores, B. typhosur and others, are very per sistent and live a long time in water. H. D. Fisher, Prof. John Tyndall and French and German bactenologists have insisted that the boiling of water at 212* F. does not destroy the spore-bearing bacteria, though it may and does destroy many other species