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
Zeroth law of thermodynamics that provides a continuous ordering of states. The dimensionality of a surface of constant temperature is one less than the number of thermodynamic parameters, thus, for an ideal gas described with three thermodynamic parameters "P", "V" and "N", it is a two-dimensional surface. For example, if two systems of ideal gases are in equilibrium, then = where "P" is the pressure in the "i"th system, "V" is the volume, and "N" is the amount (in moles, or simply the number of atoms) of gas. The surface = constant defines surfaces of equal thermodynamic temperature, and one may label defining "T"