_River Water._ This is a mixture of rain and spring water, and when deprived of the matters which it frequently holds in suspension, is generally of considerable purity. Mountain streams, which generally issue from siliceous rocks, and run over stony or pebbly beds, are, for the most part, comparatively pure and soft. The river water of New-England, and the other hilly portions of the United States, is usually of this description, though in the time of floods, and after heavy rains, they contain much sedimentary matter. River water gradually deposits much of its earthy salts as it flows, and becomes purer by exposure; it therefore generally contains less calcareous matter than spring water; its specific gravity is less, and its taste more vapid. It, however, more or less partakes of the nature of the soil over which it flows; consequently some rivers, whose waters were pure and excellent at their source, lose these properties before they mingle with the sea. The water of the Thames, for example, in England, which is originally very soft and pure, becomes so loaded with animal and vegetable matter from the towns and villages on its banks, that after being kept a month or two in a closed cask, on opening it, a quantity of sulphuretted hydrogen gas, of the most offensive odor escapes, and the water is so black and nauseous as to be unfit for use. But on racking it off, it clears, depositing a quantity of slimy mud, and becomes remarkably clear, sweet and palatable. As the matters deposited in such rivers are merely mingled with the body of the water, which is too large, and too changing, to admit of any permanent taint from solution, filtration, or even the natural deposition of the ingredients fits them for every domestic and medicinal purpose. * * * * * The following Table shows the solid contents of the Thames water[9] London, and of the Croton water[10] in the city of New-York.