where (M_W), (M_M) and (M_MW) are the molecular weights of water, methanol and the methanol/water associate respectively.

 

In a similar manner the total weight (m_i) of the mixture originally containing a volume fraction (a_i) of methanol and a volume fraction (1-a_i) of water will be

 

m_i = w_W + w_M + w_MW

 

and the density (d_i) of the mixture will be (17)

 

The additive and constitutive properties of the molar refraction of a substance has been known for nearly a century and the molar refraction is defined by the following equation,