To Make Public Water Pure.

To Make Public Water Pure.

Professor W. T. Sedgewick, the biologist of the Massachusetts State board of health, recently read a paper on “ Recent Investigations on the Purification of Public Water Supplies,” illustrated by the stereopticon.

“ Drinking water and disease,” said Professor Sedgewick, “ readily suggest each other, for, as is well known, the germs of an epidemic are often distributed by means of the water supply. But to-night I will speak not of disease, but of the way in which it may be prevented, a subject of great importance in these days when the bulk of our population is getting to dwell more and more in cities and large towns.

** As drinking water often has so much to do with the spread of disease, the question of how t« purify it and how to keep our sewage from defiling our streams, from which much of our drinking water is drawn, assumes a very great interest.

“ At Chelsea, a suburb of London, in 1839, James Simpson first tried the experiment of filtering impure water through fine sand, with the result that water was by this means rendered puie and harmless.

“ The earth is the natural purifying agent. The noxious bacteria of sewage sink into its surface and are consumed and altered into harmless materials by the bacteria of the earth. Well water, so proverbially wholesome, is the result of this simple and natural straining process.

“So successful was the experiment of Simpson that, since 1855, no water has been allowed to be distributed in London before it has been well filtered through sand. Berlin and other European cities employ similar methods of sand filtration.

“ But to our own State board of healili is due most of our scientific knowledge of the absorption of harmful bacteria by sand and gravel—what materials make the best agents for this purpose, how best to construct sand beds and the exact manner in which the absorption is carried on.

“ To Prof. Hiram F. Mills, in charge of the Lawrence experimental station, our pre-eminence is largely due. At Lawrence you may see the filtering beds five feet deep, the lower part of each of which is of coarse gravel, which, as the one gets nearer the surface, is gradually replaced by finer gravel and by sand until one gets to a surface of the finest sand. Dump into one of these beds sewage water which contains a million bacteria to the thimbleful, let it soak through and it will come out fresh and sweet, with over ninety-nine per cent of those bacteria destroyed—not a tenth of one per cent remaining.

“ Put in water which seems to the eye at least, pure, but which is really unhealthy, such as most river water, and the result will, ol course, be equally satis!actory.

“in Brockton, Framingham, Marlboro and other places, there are practical beds of this nature, beds which supply those towns with perfectly salubrious water, or which devour their sewage without offense to the senses. The sand used in these beds can, moreover, be used a wonderfully long time without cleaning or replenishing.”

The stereopticon views shown were of the sand filters in Lawrence and Framingham. In a corner of a view of the station in Lawrence, Prof. Sedgewick pointed out what he called the “cemetery experiment.” There four years ago a dog was buried and particles of the carcass are still turning up in a pool of water near by.

He also showed, by tables, something of the typhoid mortality in Chicago and Lawrence during epidemics, and traced their causes, in great measure, to the impure drinking water used. When the great epidemic occurred a few years ago in Lawrence its cause was distinctly traceable to the filth of diseased persons emptied into Stony brook, an affluent of the Merrimac above Lawrence. That same Merrimac supplied the city with drinking water at the time.

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