Amedeo Avogadro

The first hypothesis that presents itself in this connection, and which seems, besides, to be the only plausible one, is that the number of integral molecules in any gas is always the same for the same volume, or always proportional to the volumes, under the same conditions of temperature and pressure.

Thus, for example, the integral molecule of oxygen, which would be formed of two simple atoms, would be represented by O2, that of hydrogen by H2, that of nitrogen by N2, and so on.

It is clear that on this hypothesis, the relative masses of the molecules of different substances will be given by the ratios of their densities in the gaseous state, and the relative masses of the atoms will be given by the ratios of the densities of the simple gases, divided by the number of atoms in their respective molecules.

The integral molecules of gases are not formed of single atoms, but of a certain number of these simple atoms united into one.

Equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules.

The relative masses of the molecules are proportional to the densities of the gases.

The integral molecule of hydrogen is composed of two simple atoms, and that of oxygen also of two simple atoms.

The combination of one volume of oxygen with two volumes of hydrogen to form two volumes of water vapor is easily explained by supposing that the molecules of oxygen and hydrogen are diatomic.

The number of elementary molecules in a given volume of any gas is always the same, or always proportional to the volume, under the same conditions of temperature and pressure.

The integral molecules of simple gases are not formed of single atoms, but of a certain number of these simple atoms united into one.

The relative masses of the molecules are proportional to the densities of the gases, and the relative masses of the atoms are proportional to the densities of the simple gases, divided by the number of atoms in their respective molecules.

The hypothesis of equal numbers of molecules in equal volumes of gases is the only one that allows us to explain the simple ratios of volumes observed in chemical reactions.

The integral molecule of water, for example, would be formed of two atoms of hydrogen and one atom of oxygen, represented by H2O.

The number of molecules in a given volume of gas is independent of the nature of the gas, provided that the temperature and pressure are the same.

The integral molecules of simple gases are composed of at least two atoms.

The relative masses of the elementary molecules of bodies are given by the ratios of their densities in the gaseous state.

The hypothesis that equal volumes of all gases, at the same temperature and pressure, contain the same number of molecules, is confirmed by all the facts of chemistry.

The integral molecules of simple gases are formed of a certain number of simple atoms united into one.

The relative masses of the atoms are given by the ratios of the densities of the simple gases, divided by the number of atoms in their respective molecules.

The law of volumes, discovered by Gay-Lussac, finds its complete explanation in the hypothesis of equal numbers of molecules in equal volumes of gases.