ABSTRACT
One of the most interesting concepts in science is certainly the notion of gas. Even if, etymologically, the term does not appear until the 17th century, it is already present in another form during antiquity. The kinetic theory of gases aims at calculating macroscopic properties such as pressure, temperature, volume and viscosity without performing any experiment! Indeed, as its name indicates, this is a theory, and, as such, it is based on mathematical equations. In his doctoral treatise in 1873, “Over de continuiteit van den gas-en vloeistoftoestand”, van der Waals also gives a description of the phenomenon of condensation and the concept of critical temperature. Van der Waals uses the critical properties to define new variables. He calls reduced temperature the ratio of temperature over the critical temperature, reduced pressure the ratio of pressure over the critical pressure and reduced volume the ratio of volume over the critical volume.
