Practical preventive medicine . Pig. 36.—Filter bed No. i, Indianapolis Water Company. This shows work-men cleaning or scraping a filter bed to remove the muddy upper layer of sandcontaining the impurities trom the water. The sand is thrown into piles previousto being removed for washing. been previously filtered or otherwise clarified. The value ofthe process from the standpoint of the destruction of the bac-teria which pass through the filters, including pathogenic andnon-pathogenic germs, has been well demonstrated. From .1to .5 parts per million of available chlorine are commonly em-ployed
Practical preventive medicine . Pig. 36.—Filter bed No. i, Indianapolis Water Company. This shows work-men cleaning or scraping a filter bed to remove the muddy upper layer of sandcontaining the impurities trom the water. The sand is thrown into piles previousto being removed for washing. been previously filtered or otherwise clarified. The value ofthe process from the standpoint of the destruction of the bac-teria which pass through the filters, including pathogenic andnon-pathogenic germs, has been well demonstrated. From .1to .5 parts per million of available chlorine are commonly em-ployed, requiring the addition of about 5 to 12 pounds of bleachper million gallons of water. Quantities of bleach in excess of25 pounds can be detected by taste. Of recent years the employ-ment of liquid chlorine has been superseding bleach, owing to thelesser cost of the former, as well as its convenience (Fig. 43). The WATER PURIFICATION J39 1. Fig. 37.—Sand washing machine, Indianapolis Water Company. Sand beingremoved from filter bed, washed and stored by hydraulic machinery.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectprevent, bookyear1920
