Sound velocity and acoustic nonlinearity parameter for fluids. Thermodynamic premises

New theoretical formulae of the sound velocity and the B/A nonlinearity parameter for some fluids are presented in the paper. Semi--ideal and van der Waals models of gas are considered and the parameters are compared to experiment data. The liquid water model for equation of state, given by Jeffery and Austin analytical equation, is considered also and modified on the basis of acoustic data .