Speed of Sound, Density, and Related Thermodynamic Excess Properties of Binary Mixtures of 2-Pyrrolidone and N-Methyl-2-pyrrolidone with Acetonitrile and Chloroform Varfolomeev, M.A.; Rakipov, I.T.; Solomonov, B.N.; Marczak, W.; Journal of Chemical & Engineering Data 2016, 61, 1032-1046