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166. Filtering Apparatus.

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The simplest and most expeditious mode of filteration is one which Dr. Lind has described, Let a barrel with its head knocked out, be about half filled with clean sand or gravel; place a much smaller barrel without either end, or any open cylinder, upright in the middle of it, and let this be almost 333filled with the same. If the foul water be poured into the small cylinder, it will rise up through the sand of the larger barrel, and appear pure in the space between the two.