Issue 19 and Volume 20.

SANDSTONE SLABS AS FILTERS. It is generally recognized that, however useful sand filtration may be in purifying and rendering wholesome water that abounds in sewage and other pollution, imperfect and improperly conducted sand filtration loes not intercept the disease germs, and cases are given where epidemics of chc era and typhoid fever have been ascribed to the careless management of the filter beds. In consequence of the fact that the effective work of the sand filter is all done in the topmost layer of the fine sand, that impurities do not penetrate to a greater depth than a fraction of an inch, and that the deeper layers only serve to support the superficial sand, Herr Fischer, the director of the Worms (Germany) water works, conceived the idea of reducing the thickness of.the fine sand and consolidating it into slabs in order to reduce the mass of the filter. He succeeded…

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