Mathematically, this can be represented for n species as: p total = p 1 + p 2 + ⋯ ⋯ + p n = ∑ ∑ i = 1 n p i . In 1834, Émile Clapeyron combined Boyle's law and Charles' law into the first statement of the ideal gas law. Initially, the law was formulated as pV m = R (T C + 267) (with temperature expressed in degrees Celsius), where R is the gas constant. However, later work revealed that the number should actually be closer to 273.2, and then the Celsius scale was defined with 0 ∘ ∘ C = 273.15 K , giving: p V m = R ( T C + 273.15 ∘ ∘ C ) . In 1873, J. D. van der Waals introduced the first equation of state derived by the assumption of a finite volume occupied by the constituent molecules. His new formula revolutionized the study of equations of state, and was the starting point of cubic equations of state, which most famously continued via the Redlich–Kwong equation of state and the Soave modification of Redlich-Kwong.