. The principles of hygiene; a practical manual for students, physicians, and health-officers . count of the processof scraping, which is necessary to clean the filter fromtime to time, the thickness of the sand layer is reduced,and authorities differ as tothe extent of the reductionthat is permissible; someallowing a reduction to adepth of 3 decimeters;others contending that thereduction should never begreater than to 6 deci-meters before the sand isreplaced. In cleaning afilter the surface slime istaken off in a thin layerby means of a sand is then removedfrom the filter and was
. The principles of hygiene; a practical manual for students, physicians, and health-officers . count of the processof scraping, which is necessary to clean the filter fromtime to time, the thickness of the sand layer is reduced,and authorities differ as tothe extent of the reductionthat is permissible; someallowing a reduction to adepth of 3 decimeters;others contending that thereduction should never begreater than to 6 deci-meters before the sand isreplaced. In cleaning afilter the surface slime istaken off in a thin layerby means of a sand is then removedfrom the filter and washedthoroughly, when it maybe used over again. shows a section of acovered sand filter such asis in use at Albany, N. Y.,and similar in form tothose proposed for Phila-delphia and Washington. In cold climates it isnecessary to cover theniters in order to preventfreezing. In warm lati-tudes the filter should becovered over to preventundue heating of thewater. It is also advisableto cover the filters in orderto exclude sunlight andalgae, and to exclude dust. The efficiency of large sand. thus prevent the growth ofniters may be demon- 120 WATER AND WATER-SUPPLY. strated, first, by a reduced mortality from typhoid feverand from cholera after the introduction of the efficiency of sand filtration is also demonstratedmost graphically in the experience of Hamburg andAltona during the cholera epidemic of 1892, both deriv-ing their water from the river Elbe; Altona taking itssupply below the exit of the sewers of Hamburg, butfiltering its water; Hamburg using unfiltered enormous number of cases of cholera and theexplosive outbreak of the disease in Hamburg, and thecomparative freedom of Altona, are abundant evidencethat the disease was spread through the bacterial efficiency of sand filters ranges from per cent. The chemical efficiency of some of theLondon filters is such that all of the ammonia is removed,others removing f
Size: 925px × 2701px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjecthygiene, bookyear1901
