CHAPTER III.

MOLECULES AND ATOMS.

9. Molecules are Extremely Small.--It has been estimated that a
liter of any gas at 0 degrees and 760 mm. pressure contains 10^24
molecules, i.e. one with twenty-four ciphers.

Thomson estimates that if a drop of water were magnified to the
size of the earth, and its molecules increased in the same
proportion, they would be larger than fine shot, but not so large
as cricket balls.

A German has recently obtained a deposit of silver two-millionths
of a millimeter thick, and visible to the naked eye. The computed
diameter of the molecule is only one and a half millionths of a
millimeter.

By a law of chemistry there is the same number of molecules in a
given volume of every gas, if the temperature and pressure are
the same. Hence, all gaseous molecules are of the same size,
including, of course, the surrounding space. They are in rapid
motion, and the lighter the gas the more rapid the motion. This
gives rise to diffusion. See page 114.

10. We Know Nothing Definite of the Form of Molecules.--In this
book they will always be represented as of the same size, that of
two squares. A molecule is itself composed of atoms,--from two to
several hundred. The size of the atom of most elements we