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Condensation of Vapors; Distillation

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة:  P-275

2025-12-27

448

The condensation of a vapor to a liquid is brought about by lowering its temperature or by increasing the pressure upon it, or by. both. In condensing, it gives off as much heat as was required to vaporize it. It is possible to separate a liquid from substances with which it is mixed, or which it holds in solution, by boiling the mixture or solution and condensing the vapor. This process, which depends upon the difference in the boiling point of liquids, is called distillation, and the liquid that has been purified by it is called the distillate. The condenser, in which the condensation takes place, may be in the form of a straight tube, as in Fig. 1, or in the form of a spiral tube, which is called a worm. Each form is surrounded by a water jacket to keep the tube cool. The purity of the distillate is increased by redistillation. In a mixture of alcohol and water, for example, a little water comes over with the alcohol in the first distillation, but less in the second.

Demonstration. - Arrange apparatus as shown in Fig. 1. Pass cold water in at the lower end of the water jacket and let it run out at the top. Put a mixture of equal parts of alcohol and water in the flask. Boil it until about a third of the mixture is condensed in the beaker. Remove the flame and test the distillate by setting it on fire. Test the mixture remaining in the flask in the same way.