PURIFICATION OF WATER SUPPLIES.
This is so important that it must be considered at some length and under several subheadings. Enough has al ready been said to show that nearly all waters in their natural or raw state are unsuitable for potable uses, hut most unpolluted surface waters may be rendered wholesome. Under this subtitle some of the processes in use for that purpose will be described.
Purification of water supplies is no longer effected by the lyre of Empedocks as stated by Matthew Arnold, whose music did Cassats to sweet sin the breath at pouocous susaia." Absolute self-purification of running waters has not been conclusively demonstrated. though partial purification is undoubtedly effected. (Consult Phelps, Earle B., 'Studies on the Self Purification of Streams,' United States Public Health Service). Where oxygen from the air is dissolved in water oxidation of organic matter takes place and bacteria in time are destroyed provided such running water be not further pol luted by sewage and other contaminating refuse. Where waters are covered with ice and oxygen is excluded therefrom, there may be an increase in their bacterial content. Prof. H. Marshall Ward has that the blue and violet rays of sunlight destroy bacteria near the sur face hut have little or no effect upon the germs a few feet below the surface. In darkness some genera are The B. cote cow rresmis, B. will live several days in running water and multiply therein, if there be waste material thrown into it.
To aid natural purification, 'filter wells,' •filter galleries' and •filter cribs' have been installed at some places in West Virginia. Penn sylvania, Indiana, Ohio. Massachusetts and else where, which are of doubtful utility for they merely clear the water of visible pollution, while they may concentrate the bacteria 'owl promote their propagation.
Polluted waters percolating into some soils are subjected to nitrification, which William P. Mason describes, as the tearing asunder of the objectionable nitrogenous organic materials, securing their union with the oxygen of the air and thus converting them into harmless inor ganic The action of nitrifying bacilli is mainly confined to upper layers of soil.
Mason on 'Water Supply.' p 221 George A. Johnson of the United States
Geological Survey says in his valuable Water Supply paper that •a majority of the cities and towns of the United States take their water supply from ground sources .
and as a rule they are pure, clear and less, although they are very hard and others contain much iron in solution.* Recent bac teriological and microscopic examinations, how ever, show many ground waters and conse quently wells and springs are not wholly free of pathogenic bacteria. All waters collected for potable purposes ought to be tested before they are used Most of them in their natural state contain micro-organisms, some of which are pathogenic and others are harmless as stated by Dr. Maximilian Marsson of Berlin in his lectures on *The Significance of Flora and Fauna in Maintaining the Purity of Nat ural Waters.' Each water supply from what ever source ought to be tested before use. Iron is found in the ground waters of Ger many, Holland, the Netherlands, Britain, the United States and elsewhere.
In his valuable work entitled Purifica tion of Public Water Supplies,' John W. Hill, at page 278, says 'the dimensions of the bacteria (B. typhosi) are stated in microns, designated by the Greek letter which is 1/1000 milli meter, equal to 1/25000 of an inch. Thus the typical dimensions of B. typhosus are .5 to .8 wide, by 1.5 to 2.5 is long, or about 1/50000 to 1/31250 of an inch wide or thick and 1/16666 to 1/10000 of an inch long. Tak ing the average length of the typhoid bacillus as two microns (es) it would require 12,500 of these placed end on end to make an inch.' All such bacteria are invisible and may be de tected only by some one of the modern scien tific tests. (Consult Hasseltine, H. E., (The Bacteriological Examination of Water,' United States Public Health Service). Some bacteria are non-pathogenic and. with such knowledge as we now have of their characteristics, are con sidered harmless, while others are themselves destructive of lower bacteria, as are the Roliferu. Bacteriologists are studying these lower forms of life to determine their nature and activities in relation to other forms of animal life and are making new discoveries from time to time of vital importance to the welfare of the race.