Avogadro constant [SEP] named after
determined experimentally for each substance.
History.
History Origin of the concept.
The Avogadro constant is named after the Italian scientist Amedeo Avogadro, who, in 1811, first proposed that the volume of a gas (at a given pressure and temperature) is proportional to the number of atoms or molecules regardless of the nature of the gas.
The name "Avogadro's number" was coined in 1909 by the physicist Jean Perrin, who defined it as the number of molecules in exactly 32 grams of oxygen. The
Boltzmann constant
The Boltzmann constant ( or ) is a physical constant named after its discoverer, Ludwig Boltzmann, which relates the average relative kinetic energy of particles in a gas with the temperature of the gas and occurs in Planck's law of black-body radiation and in Boltzmann's entropy formula. 
It is the gas constant divided by the Avogadro constant :
The Boltzmann constant has the dimension energy divided by temperature, the same as entropy. 
Before 2019, its value in SI units was a measured quantity.