The Romance of Modern Chemistry

NATURAL WATERS lower temperatures, and thereby passes from the con- dition of a gas to that of a liquid, and from the con- dition of a liquid to that of a solid, it shrinks and becomes more dense—that is, a given bulk of the substance weighs more and more. Water, however, is peculiar. As the temperature falls, it changes from steam to liquid water and from liquid water to ice, but there is not through- out these changes a continuous increase of density Water does indeed become more and more dense down to a certain point, 89° Fahrenheit, but here it reverses its behaviour; it expands and becomes lighter as it gets colder. So it comes about that ice is lighter than the water from which it freezes, and accordingly floate on the surface of the water. A little thought will show how significant this fact is in the economy of Nature for the preservation of life in our lakes and seas during a severe winter is possible only because the surface ice protects the water underneath from freezing. The same fact, however beneficial in its consequences in the realm of Nature, is liable to put us moderns sometimes to considerable inconvenience. We fit our houses with water-pipes, and it is only when the grip of winter has been unusually severe and our pipes are burst, that we learn that Nature will have her way in spite of our devices. Since ice occupies more space than the same weight of water, the pipes are burst when the water freezes, although it is not till the thaw comes that the damage is revealed to us. Now the waters with which Nature supplies us, not always very regularly, according to our way of thinking, arc never pure from the chemist’s point of view. Many of them are fresh and quite suitable for drinking purposes, but even they contain substances which make them a little 97 o