Absolutely or chemically pure water is never found in nature. Absolutely pure water consists of a chemical combination of two volumes of hydrogen with one of oxygen gas, containing absolutely nothing else.

The words pure water are used in two distinct senses. The scientific chemist uses them to describe water which is nothing but water; the public and the scientific chemists, too, use them to describe water which is not impure, but which may contain small quantities of many harmless, nay useful, dissolved solid and gaseous substances.

It is probable that no person has ever drunk a single half pint of pure water; that is, chemically-pure water. Probably not one person in ten thousand has ever seen chemically-pure water, and not one in a 2 million seen more than a few drops bedewing the inner sides of a closed bottle. When a scientist closed up the two elements of water, namely, pure hydrogen gas and pure oxygen gas in a bottle, and ignited the mixture, a film of moisture was seen inside the glass; and if the operation was several times repeated, a few drops were perhaps collected within the vessel. This was pure water, though, indeed, we should make no mere trivial assertion if we said that even this apparently chemically pure water would contain traces of alkali dissolved from the glass, or would contain in solution traces of either free hydrogen, free oxygen, or even air, the presence of which is unavoidable by human manipulators.

Fig. 4.   condenser and Filter

Fig. 4. - condenser and Filter.

Fig. 5.   Plan, Condenser and Filter

Fig. 5. - Plan, Condenser and Filter.

A, Steam inlet; B, Outlet to filter; C, Circulating water inlet; D, Circulating overflow; E, Distilled and filtered water outlet; F, Relief pipe G, Animal charcoal filter.

For all practical purposes, however, even for those of exact chemical analysis, when water is thus produced from its pure elements, out of contact of air, it is pure water.