On the Influence of various Substances in Accelerating the Precipitation of Clay suspended in Water

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Abstract
I t has been noticed by several observers that clay suspended in water settles more quickly if the water is salt than if it is fresh. This fact is contrary to what would naturally be supposed—namely, that suspended matter should settle more easily in a liquid of low than in one of high specific gravity. The earliest notice which I have been able to find relating to this subject, is a note by Skey in the ‘Chemical News’ for 1868, p. 160, in which he advances the following hypothesis to explain the phenomenon. After taking notice of the fact that those salts which accelerate the precipitation of clay are too stable to be decomposed, by mere contact with it, he suggests that such salts have a strong affinity for water compared with that of clay for water. They therefore tend to abstract water from the clay, and cause it to coagulate and settle. In corroboration of this he instances the fact that iron ferrocyanide is thrown down by numerous salts; that silica is precipitated from its solution in ammonia by chloride of ammonium; and that nitrate of baryta is precipitated by nitric acid. In the ‘Chemical News’ for August, 1874, Durham advances an electric hypothesis; he supposes that clay, in falling through water, “generates electricity by friction, and, as water is a bad water remains for some time, hence they are mutually attracted; but when an acid or salt are added, the liquid becomes a good conductor, the potentials are equalized

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