. Public health and preventive medicine. ated. /,Loose filtrant. </. liaised part of diaphragmto assist How. h, Water shower, i, Filteredwater, j, Tap. ill the form of block or powder, andboth may be combined (Fig. 117).Sponge and flannel, being organicmaterials, should never be iron, as used in Bischofs filter(Fig. 118), is excellent, but the arrange-ment is complicated, owing to the factthat a little iron passes into the waterand has to be removed by subsequentpassage through sand and oxide of man-ganese. Apart from adding iron, thisfilter removes organic matter, lessensha
. Public health and preventive medicine. ated. /,Loose filtrant. </. liaised part of diaphragmto assist How. h, Water shower, i, Filteredwater, j, Tap. ill the form of block or powder, andboth may be combined (Fig. 117).Sponge and flannel, being organicmaterials, should never be iron, as used in Bischofs filter(Fig. 118), is excellent, but the arrange-ment is complicated, owing to the factthat a little iron passes into the waterand has to be removed by subsequentpassage through sand and oxide of man-ganese. Apart from adding iron, thisfilter removes organic matter, lessenshardness, and may reduce nitrates toammonia. Magnetic carbide of iron isa carbide of iron pulverised and mixedwith sand. The carbide is obtainedby roasting red haematite and sawdusttogether in a retort. It has not thedisadvantages of charcoal, but is not sogood as spongy iron. Carferal con-sists of iron, charcoal, and clay, and is said to answer well. < »ther mix-tures containing charcoal are manganous carbon (charcoal and black oxide. I llllllllllliniiimiv, Trrr*//, Fig. 118.—Spongy iron filter, a, Unfilteredwater, h. Spongy iron, c, Sand, d,Filtered water ready for aeration, e,Regulator. /, Water shower, d1, Aeratedfiltered water, g, Tap. WATER SUPPLY 337 of manganese), earbalite, used in Creases ship filter, and Maignens filtrerapide (charcoal, lime, and asbestos). Asbestos forms a good medium, andcan be readily purified by means of fire. With regard to all filters, itmay be said, that while frequently of value they tend to engender a falsefeeling of security as regards micro-organisms, and one should aim atsecuring a pure water supply rather than a good filter. Boiling is thesurest way of rendering a drinking-water safe, but it makes it less palat-able by driving off the contained gases. At the same time it lessens tem-porary hardness. The addition of lime or washing soda also lessens hard-ness, while effluvia and much of the dissolved and suspended organic mattercan be
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectprevent, bookyear1902
