The difference between a gas and a liquid is that in the former, the atoms and molecules move to and fro in an independent existence, whereas in the latter, they are always in touch with one another, though they are changing partners continually.

The infinite variety in the properties of the solid materials we find in the world is really the expression of the infinite variety of the ways in which the atoms and molecules can be tied together, and of the strength of those ties.

When a liquid boils, the temperature has been raised to such a pitch that the evaporating molecules are sufficient in number and speed to lift off the air from the surface of the liquid and push it back en masse.

William Henry Bragg Quotes