ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2012, Vol. 86, No. 8, pp. 1204–1207. © Pleiades Publishing, Ltd., 2012. 1204 1 INTRODUCTION Ultrasonic velocity affects the physical properties of the medium and hence one can furnish information about the liquid and liquid mixtures. In recent years, ultrasonic velocity is gaining importance in under- standing the nature of solute-solvent interactions [1]. Knowledge of thermodynamic and acoustical proper- ties is of great significant in studying the physical behavior and molecular interactions in a variety of liq- uid mixtures of pure [2, 3], liquid mixtures [4–6] and electrolytic solutions [7–10]. A survey of literature shows that scanty work has been done on binary mix- tures of phenol with some organic liquids [4, 5]. The present work reports evaluation of some acoustical parameters of ternary mixtures of toluene + chloro- form + cyclohexane at 303.15, 308.15, and 313.15 K. The adiabatic compressibility, intermolecular free length, free volume, internal pressure, acoustical impedance, Rao’s constant and Wada’s constant of mixtures at various temperatures haven been studied in the present paper. Such data are expected to high- light the role of solute and solvents in the solutions and its influence on temperature. EXPERIMENTAL The ultrasonic velocity in the liquid mixtures have been measured using an ultrasonic interferometer 1 The article is published in the original. (Mittal type-82, New Delhi, India) working at 2 MHz frequency with accuracy ±0.1 m s –1 . The interferometer is a fixed frequency variable path type. Ultrasound of constant frequency is generated at the bottom of the cylindrical sample cell using quartz crystal and is sent into the medium under study. The propagated waves after getting reflected at the reflector surface held at the top of the cell, again travels back through the same medium. These two waves form stationary wave pattern and hence nodes and antinodes are formed in the medium. A fine micrometer screw is provided in the set up that allows for finer movements of the reflector plate in the medium. Thus moving the reflector plate for a fixed number of antinode (or node) positions, the dis- tance moved for a known number of waves can be known. Use of frequency with these data will yield the sound velocity in the medium. The density and viscosity are measured using a pycnometer and an Oswald’s vis- cometer of accuracy of ±0.1 kg m –3 and 0.001 m N cm –2 respectively. The samples are Anala2R grade of purity 99.5% and used directly with out purification. The val- ues of density, viscosity and velocity of pure samples are agreed well with the standard reference values. In all systems, the mole fraction of the second compo- nent, chloroform (x 2 = 0.2) was kept constant, while the mole fraction of the remaining (x 1 and x 3 ) were varied from 0.1 to 0.8 as to have the different compo- sitions [11]. Acoustical Parameters of Toluene + Chloroform + Cyclohexane Mixtures at 303.15, 308.15, and 313.15 K 1 V. Vanathi a , S. Mullainathan a , and S. Nithiyanantham b a Department of Physics, AVC College of Engineering, Mayiladuthurai, Tamil nadu, India 609306 b School of Physical Sciences and Nanotechnology, (Biophysics/Ultrasonics Division), SRM University, Kattankulathur, Tamil nadu, India 603203 E-mail: s_nithu59@rediffmail.com Received March 5, 2011 Abstract—Ultrasonic velocity, density and viscosity of the ternary mixture of toluene + chloroform + cyclo- hexane, were measured at 303.15, 308.15, and 313.15 K. The thermodynamically parameters such as adia- batic compressibility (β), intermolecular free length (L f ), free volume (V f ), internal pressure (π i ), acoustic impedance (Z), molar sound velocity (R), and molar compressibility (W) have been obtained from the exper- imental data for all the mixtures, with a view to investigate the exact nature of molecular interaction. Adia- batic compressibility and intermolecular free length decrease with increase in concentration and tempera- ture. The other parameters show almost increasing concentration of solutes. These parameters have been fur- ther used to interpret the molecular interaction part of the solute and solvent in the mixtures. Keywords: ultrasonic velocity, organic liquids, acoustical properties, molecular interactions. DOI: 10.1134/S0036024412060295 PHYSICAL CHEMISTRY OF SOLUTIONS