EFFECTS OF HEAT.
They are four in number. Rise of temperature, expansion, liquefaction, evaporation. The first indication of the presence of heat is discovered by an elevation in temperature. Though man is not a reliable thermometer, he would be able, ordinarily, even if blind, to chronicle the progress of the sun, from horizon to horizon, by the increasing and decreasing warmth. The little thermometer placed beneath the tongue of the invalid gives reliable report of the combustion going on within his system. We see a thousand illustrations of the expansive effects of heat, many of which are familiar to all. The exceptions are more interesting than the rule, and less known, the ordinary rule being that heat expands and cold (absence of heat) contracts. Water contracts by cold until it reaches the temperature of 39°, and then expands with great violence until congelation is completed, at 32°. A British officer in Quebec filled a twelve inch shell with water, and closed the fuse hole with a wooden plug securely driven in with a mallet. Upon being exposed to intense cold the plug was projected a distance of several hundred feet, and a long tongue of ice was found protruding from the opening.
It is supposed that sufficient heat would convert all solids first into liquids, and then into gases. In the process of distillation, if we wish to retain its products, we combine both heating and cooling.
The knowledge of the melting and vaporizing point of substances is of immense value. We are enabled thus to drive off and secure the various ingredients entering into many complex substances. A notable instance is seen in the means used to secure the rich and varied products of petroleum.