Amedeo Avogadro

The study of these proportions appears to me to be one of the most important problems of chemistry.

The different quantities of the same element contained in different molecules are all whole multiples of one and the same quantity.

We must distinguish between molecules of the same substance and atoms of the same element.

The laws of combination in definite proportions are a necessary consequence of the molecular theory.

The volumes of gases which combine are in a very simple ratio to each other.

The facts of chemistry are inexplicable without the notion of molecules.

The determination of the relative masses of molecules is the foundation of all stoichiometry.

The physical properties of gases depend on the number of molecules present, not on their nature.

If one accepts the hypothesis I have proposed, the results of Gay-Lussac on the combination of gases by volume become clear.

The constancy of this number (Avogadro's constant) provides a link between the macroscopic and microscopic worlds.

The simplicity of nature often reveals itself in numerical constancy.

A gas expands to fill its container because its molecules are in constant, rapid motion.

In scientific research, a hypothesis is not to be considered true until it is confirmed by numerous experiments.

The progress of chemistry depends on precise measurement and bold conceptualization.

The distinction between atoms and molecules is fundamental to understanding chemical reactions.

Without a clear conception of molecular proportions, chemistry remains a collection of unrelated facts.

The air we breathe is a mixture of gases whose molecules are widely separated.

It is remarkable that so many gaseous reactions occur in simple volume ratios.

The molecular theory provides a unifying principle for the whole of chemistry.

The weight of a liter of any gas, under standard conditions, is proportional to the weight of its molecules.