Purification of Water.

다국어 초록 (Multilingual Abstract)

If we add a small portion of clay to a tumbler of clean water, stir it well up, we all know that it will become colored and turbid. This affords a simple illustration of the mechanical suspension of bodies in water. When at rest these particles, if specifically heavier than water, will settle to the bottom; if lighter, will float on the top. Some few substances, indeed, having about the same specific gravity, will remain mixed with it until, as generally happens, some molecular change occurs in them, rendering them lighter or heavier than an equal bulk of water, when, of course, they float or sink, as may be.