Elements of Field Hygiene and Sanitation by Joseph Herbert Ford

Author:Joseph Herbert Ford
Language: eng
Format: epub, pdf
Publisher: Blakiston
Published: 1918-03-25T05:00:00+00:00

filtration. The apex of the cone receives the sedi-

filter employs two powders, the first consisting of

m alum, potassium permanganate, aluminum silicate, the

:hiefly of aluminum silicate and small amounts of tannic and

iloric adds. After the filter has been filled a suitable quan-

5ELF CLEANI^G FILTER

LEAR 'ATER

Fig. 113.—Sand and alum filter. (After Leltan.^

:y of the first powder (enough to plainly discol ided and stirred up. After a few minutes atiout 0 E the second powder is added and stirred until t aused by the first has been removed. After the ides, in 15 or 20 minutes, the leather spouts are

nent camps thb pit may be lined with wattle work, or a barrel, keg or box, from which both ends have been removed.

Several other more elaborate devices utilize the straining effect of aluminum hydrozid. The best of these is the Darnall filter, which consists of a syphon with a cylindrical metal framework sui' rounding its ascending arm; a cloth which surrounds this framework and is the essential part of the filter; a syphon primer, two water cans, a galvanized iron tank and a crate. The precipitant consists of alum bydioxid and sodium carbonate in proportions which satisfy each other chemically. Five grains of alum to the gallon are suffi-

PlG. 113.—Damall filter in operation. *

cient to dear the most grossly polluted water. When the precipitant is added to water a flocculent precipitate is formed which entangles parasites and arrests them on the surface and in the body of the filtering dolh. This becomes clogged eventually and must be removed and brushed, but as the output continues to diminish, the cloth is removed, washed, boiled and dried. Meanwhile it is replaced by another. This apparatus removes 98 per cent, of the bacteria in water; clarifies it and will deliver 50 gallons of water an hour. It weighs 53 pounds, and is quite the best apparatus yet devised for filtering water in the field.

The Japanese field filter (the Ishiji filter) consists of a conical canvas bag having a capacity of 24 gallons and with two spouts or branches just above the ^es. These spouts contain sponge di^

which effect filtration. The apex of the cone recdves the sediment. This filter employs two powders, the first consisting of

potassium alum, potassium permanganate, aluminum silicate, the second chiefiy of aluminum silicate and small amounts of tannic and hydrochloric acids. After the filter has been filled a suitable quan-

SELF CLEANING FILTER

LEAR ATER

Pic. 113.—Sand and alum filter, (Afltr Lttean.)

tity of the first powder (enough to pldnly discolor the water) is added and stirred up. After a few minutes about one-half as much of the second powder is added and stirred until the discoloration caused by the first has been removed. After the precipitate subsides, in 15 or 30 minutes, the leather spouts are untied and the

water allowed to pass. The hydrochloric acid assists the decomposition of the permanganate while the tannic acid removes the color. The result is satisfactory with clear water but much less so with turbid water. A modification of this

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