Gay-Lussac's law gases and the gaseous products can be expressed in simple whole numbers. For example, Gay-Lussac found that 2 volumes of hydrogen and 1 volume of oxygen would react to form 2 volumes of gaseous water. Based on Gay-Lussac's results, Amedeo Avogadro theorized that, at the same temperature and pressure, equal volumes of gas contain equal numbers of molecules (Avogadro's law). This hypothesis meant that the previously stated result could also be expressed as The law of combining gases was made public by Joseph Louis Gay-Lussac in 1808. Avogadro's hypothesis, however, was not initially accepted by chemists until the Italian chemist
History of molecular theory Determining the Relative Masses of the Elementary Molecules of Bodies", he essentially states, i.e. according to Partington's "A Short History of Chemistry", that: Note that this quote is not a literal translation. Avogadro uses the name "molecule" for both atoms and molecules. Specifically, he uses the name "elementary molecule" when referring to atoms and to complicate the matter also speaks of "compound molecules" and "composite molecules". During his stay in Vercelli, Avogadro wrote a concise note ("memoria") in which he declared the hypothesis of what we now call Avogadro's law: "equal volumes of gases, at the same temperature and pressure,