Page:Elementary Text-book of Physics (Anthony, 1897).djvu/97

 CHAPTER III.

MOLECULAR MECHANICS.

CONSTITUTION OF MATTER.

65. General Properties of Bodies.— Besides the properties already defined in § 3 as characteristic and essential properties of matter, we find that all bodies possess the properties of compressibility and divisibility.

Compressibility.— All bodies change in volume by change of pressure and temperature. If a body of a given volume be subjected to pressure it will return to its original volume when the pressure is removed, provided the pressure has not been too great. This property of assuming its original volume is called elasticity. The property of changing volume by the application of heat is sometimes specially called dilatability.

Divisibility.—Any body of sensible magnitude may, by mechanical means, be divided, and each of its parts may again be subdivided; and the process may be continued till the resulting particles become so minute that we are no longer able to recognize them, even when assisted by the most perfect appliances of the microscope. If the body be one that can be dissolved, it may be put in solution, and this maybe greatly diluted; and in some cases the body may be detected by the color which it imparts to the diluent, even when constituting so small a proportion as one one-hundred-millionth part of the solution.

66. Molecules.—We are not, however, at liberty to conclude that matter is infinitely divisible. The fact, established by observation, that bodies are impenetrable, and the one just noted, that they are also compressible, as well as other considerations, to be adduced later, lead to the opposite conclusion. To explain the