Physicochemical studies of homoeopathic formulations (extremely diluted solutions) of acidum salicylicum in ethanol by using volumetric, acoustic, viscometric and refractive index measurements at 298.15, 308.15 and 318.15 K Anil Kumar Nain a, ⁎, Preeti Droliya a , Raj Kumar Manchanda b , Anil Khurana b , Debadatta Nayak b a Department of Chemistry, Dyal Singh College, University of Delhi, New Delhi 110 003, India b Central Council for Research in Homoeopathy, Ministry of AYUSH, Govt. of India, New Delhi 110 058, India abstract article info Article history: Received 8 December 2015 Received in revised form 6 January 2016 Accepted 11 January 2016 Available online xxxx The densities, ρ, ultrasonic speeds, u and viscosities, η and refractive indices, n D of pure ethanol, 15 samples of succussed ethanol controls, 15 formulations of acidum salicylicum in unsuccussed ethanol and 15 formulations of acidum salicylicum in succussed ethanol have been measured for potencies from 2 C to 30 C (with an interval of 2 C) at 298.15, 308.15 and 318.15 K and atmospheric pressure. From these experimental data, the isentropic compressibilities, κ s , intermolecular free length, L f , acoustic impedance, Z, relative association, R A , excess isentro- pic compressibility, κ s E , excess intermolecular free length, L f E , excess acoustic impedance, Z E , excess viscosity, η E and excess refractive index, n D E have been calculated. The results have been qualitatively discussed in terms of in- teractions/physicochemical behaviour of acidum salicylicum in these solutions. The results indicate that even in extreme dilutions the molecules of acidum salicylicum may be present in these homoeopathic formulations. Both the presence of acidum salicylicum as well as succussion phenomenon may be responsible for the variation of the physicochemical properties of these homoeopathic formulations. © 2016 Elsevier B.V. All rights reserved. Keywords: Density Ultrasonic speed Viscosity Refractive index Extremely diluted solutions Homoeopathic medicines 1. Introduction Homoeopathy is one of the established and most popular alternative systems of medicine, and is considered second to conventional therapy around the world. The homoeopathic medicines are “extremely diluted solutions” exhibiting anomalous behaviour in their properties and effi- cacy. The homoeopathic medicine formulations are generally obtained through a combination of two processes: a dilution of 1:100 in mass followed by succussion. The effectiveness of homoeopathy is well sup- ported by research evidences; however, there have been controversies regarding improbability in biological activity of homoeopathic medi- cines in which the source drug is diluted beyond Avagadro's number; as such medicine formulation must be identical to the solvent. There have been few investigations pertaining to find the presence of drug in extremely diluted formulations [1–5], but the questions still remains to be answered satisfactorily. Physicochemical properties of solutions containing solutes like amino acids, electrolytes, carbohydrates, drugs, etc. have been found helpful in the characterization of solute–solute and solute–solvent interactions, which are useful in understanding of solute–solvation/ hydration behaviour of solute and preferential solvation of solute by the solvent [6–15]. Physicochemical methods are important be- cause the changes in properties caused by variation of composition, temperature and pressure and can be investigated without any refer- ence to assumption models or hypothesis. Since homoeopathic for- mulations are extremely dilute solutions, their physicochemical properties, viz., density, ultrasonic speed, viscosity, refractive index, etc. can be measured easily as functions of concentration and tempera- ture. The physicochemical parameters derived from these experimental data can provide valuable information for the understanding of physi- cochemical behaviour/interactions of homoeopathic medicines and mechanism of their action. Recently, there have been few physicochem- ical studies on extremely diluted solutions of inorganic salts [16–21] and homoeopathic medicines [22–27] by using calorimetric and con- ductometric methods. These studies provided interesting and convinc- ing information on the behaviour of these extremely diluted solutions. To the best of our knowledge, no systematic physicochemical studies on homoeopathic medicines using volumetric, acoustic, viscometric and optical methods have been reported in the literature, except our re- cent study [28] on homoeopathic formulations (extremely dilute solu- tions) of sulphur in ethanol. In continuation to our earlier study [28], here we report the results of the physicochemical study on extremely Journal of Molecular Liquids 215 (2016) 680–690 ⁎ Corresponding author. E-mail address: ak_nain@yahoo.co.in (A.K. Nain). http://dx.doi.org/10.1016/j.molliq.2016.01.032 0167-7322/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq