The Romance of Modern Chemistry

NATURAL WATERS of such a spring, it is gradually impregnated and coated with a stony-like substance. The explanation is that the water of a petrifying spring is hard, and contains a con- siderable quantity of carbonate of lime in solution. When the water comes to the surface it deposits carbonate of lime, because it loses by evaporation some of the carbon dioxide in virtue of which it has the power of dissolving that substance. This deposition of calcareous matter may take place on any objects, such as leaves or twigs, exposed to the play of the water, but it is thought by some people that certain bog-mosses or water-plants are specially effective in causing decomposition of the carbonic acid, and thereby inducing the deposition of a crust of carbonate of lime on their stems and branches. Most of the water which has percolated through the soil and the rocks, and thereby collected a certain amount of solid matter, finds its way into streams and rivers and ultimately into lakes and seas. It will be obvious that the amount of solid matter in the sea and in lakes which have no outlet must be gradually increasing, since the supply of water is roughly balanced by continual evaporation from the surface. The rate of increase of the solids in sea water is very small because of the enormous quantity of water, but in the case of an inland lake in a hot climate, where there are heavy rains alternating with periods of rapid evaporation, the amount of dissolved solid is very high and increases fairly rapidly. The Dead Sea is a case in point Its waters are exceedingly brackish, and contain no less than about a quarter of their weight of solid matter, mostly sodium chloride (common salt) washed out from the neighbour- ing hills. The presence of so much solid makes the 101