The Romance of Modern Chemistry

NATURAL WATERS water of the Dead Sea considerably heavier, bulk for bulk, than fresh water; it is so dense that eggs will float in it, and it will not allow the human body to sink. Ordinary sea water also is somewhat denser than fresh water, and its superior buoyancy is possibly known already to the reader by personal experience. Much of the water which is distributed over the surface of the globe is quite unsuitable for the use of man. All brackish waters come under this category; and many an unfortunate sailor who has been cast adrift at sea has realised the bitter truth that there was “ water everywhere, but not a drop to drink.1’ Even from sea water, however, it is possible to obtain pure water by the process of distillation. The water is boiled in a suitable vessel, and the steam is led away through a cooled pipe, at the end of which the condensed water may be collected in a pure state. The solids dissolved in the sea water are not volatile, and are accordingly left behind in the boiler. At the present day much of the fresh water required on board our great ocean liners is obtained by subjecting sea water to distillation. When one thinks of it, Nature herself is constantly making use of this process. The evaporation that continually takes place from the surface of the ocean is really a slow distillation; the water vapour condenses into clouds, and falls, some of it at least, as rain on the surface of the land. Rain is natural distilled water. For many domestic and industrial purposes it is necessary to purify even ordinary fresh water, especially when it is hard. This process of “softening” water may be effected in several ways. It has already been stated that mere boiling will diminish the hardness of a water, but even water that has been boiled will not 102