232 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME 5. Mow \v(Hil(l yuu cluingt.' water va|)or into li(jui(J water? 6. Define the following processes, and state whether the process liberates or absorbs heat: \ai)orization, melting, sublimation, distillation, freezing, condensation. 7. What is the princij^le of mechanical refrigerators? 8. What is the principle of the gas refrigerator? 9. Why does water boil at a lower temperature on a mountain than it does at sea level? 10. What is \apor pressure, and how may it be measured? 11. E.xplain the principle of pressure cookers and autoclaves. 12. Mention two applications of the high heat of vaf)orization of water.
UNIT IV SECTION 5 PHYSICAL PROPERTIES AND PHYSICAL PROCESSES ARE EXPLAINED BY THE KINETIC-MOLECULAR THEORY Introduction. The properties of gases, liquids, and solids and the physical processes by which matter changes from one state to another are generally accepted without question. No one doubts the correctness of Boyle's Law, Graham's Law, and Charles' Law, although it is recognized that they are not exact laws but approximations only. It was not until the kinetic-molecular theory was evolved that man was able satisfactorily to explain the properties of gases, liquids, and solids and understand the laws dealing with physical changes. The kinetic-molecular theory is one of the great theories of physical science. For that reason it is important that we pause here to study this theory and see how beautifully it explains so many phenomena and aids in the prediction of the outcome of the untried experiments. Turn to Unit I, Section 3, and review the portion dealing with the nature and function of theories. Many Men Contributed to the Development of the Kinetic-molecular Theory. Sir Francis Bacon (1561-1626), impressed by the failure of scholasticism to advance knowledge, advocated the use of a more scientific method. His method of attack involved extensive observations, recording of available observations, carrying out experiments suggested by these observations as far as possible, and then formulating general laws which show the relationships between these observations. In experimenting with a pan filled with sand. Bacon observed that heavy particles rested on the surface of the sand when the pan was at rest. As soon, however, as the sand was shaken, the heavier particles worked their way to the bottom; in other words, the sand behaved very much as a liquid in its inability to support a body more dense than itself. Bacon, himself, accomplished little in actual experimental work, but the method he advocated is said to have influenced Robert Boyle. 233