Additive molar functions for sound propagation

In Chap. 10 we have seen that the relative speed of light waves (i.e. the ratio of the speed in vacuum to that in a material), alias the refractive index (n), can be related to a temperature-independent material constant the specific refraction (n — l)/p. Multiplied with the molar mass this gives the Molar Refraction R  

A set of additive group contributions for UR valid for liquids was derived by Sakiades and Coates (1955). 

The Rao function has the same form as the Sugden function or Molar Parachor (Ps = My1/4/p), derived by Sugden in 1924, which correlates the surface tension with the chemical structure. Also the Small function or Molar Attraction Function, which correlates the cohesion energy density, ecoh, and the solubility parameter, 8, with the chemical structure, has this form  

In solids the situation is more complicated than in liquids. Here we have two types of waves, viz. the longitudinal and the shear waves. In contrast with liquids the longitudinal wave in solids is not only determined by the bulk or compression modulus but also by the shear modulus, or alternatively by the Poisson ratio. 

Schuyer (1958,1959) proved that instead of the simple relationship w2 = K/p, valid for liquids, a more complicated expression must be used in the case of solids  

---