RT Journal
T1 TYphoid fever and mechanical filters
JF Journal of the American Medical Association
JO Journal of the American Medical Association
YR 1909
FD April 24
VO LII
IS 17
SP 1337
OP 1337
DO 10.1001/jama.1909.02540430033006
UL http://dx.doi.org/10.1001/jama.1909.02540430033006
AB As is well known, there are two principal methods in use in this country for purifying public water supplies. The older of these is the slow sand filtration method practiced for many years in England, Holland and Germany, and long proved to be an efficient safeguard against water-borne infections. When this system is employed with relatively clear waters the difficulty and expense of operation, due largely to the frequent scraping-off of the surface layer of sand, are not great, but if a very turbid water has to be treated the rapid clogging that results makes the filter practically unworkable. Muddy waters, therefore, are usually clarified by the addition of suitable chemicals, such as aluminum sulphate. Many special forms of apparatus for this purpose have been devised and are in use in different parts of the United States. They all agree in providing for mixing the chemicals with the water in