Page:Elementary Text-book of Physics (Anthony, 1897).djvu/256

242 other gases can be found by dividing this velocity by the square root of the ratio of their masses to the mass of the molecule of hydrogen, or by the square roots of their molecular weights divided by 2.

From calculations based on the behavior of gases with reference to their viscosity and thermal conductivity, Maxwell deduced a number of conclusions respecting the dimensions and motions of molecules, which are given in the following table. The symbol $$\mu\mu$$ denotes a micromillimetre, or the millionth of a millimetre.

The number of hydrogen molecules in a milligram is about 200 million million million, and about 2 million could be placed side by side in one millimetre. The number of molecules of hydrogen, and so also of any other gas, in one cubic centimetre at the standard pressure and temperature is about 19 million million million.

From the experiments of Quincke and Reinhold and Rücker the range of molecular action is estimated to lie between 50 $$\mu\mu$$ and 118 $$\mu\mu.$$ The molecular forces give rise to pressures in the gas which van der Waals estimates as, for hydrogen, 0; for air, 0.0028; for carbon dioxide, 0.00874.

Other calculations yield values for these various molecular constants which, while not numerically the same as those of Maxwell, are yet of the same order of magnitude, and considerable confidence can be placed in their general accuracy.