Journal of Thermal Analysis and Calorimetry, Vol. 78 (2004) 331–342 NEW PHYSICO-CHEMICAL PROPERTIES OF EXTREMELY DILUTED AQUEOUS SOLUTIONS A calorimetric and conductivity study at 25°C V. Elia 1* , E. Napoli 1 , M. Niccoli 1 , L. Nonatelli 1 , A. Ramaglia 2 and E. Ventimiglia 1 1 Department of Chemistry, University ‘Federico II’ of Naples, Complesso, Universitario di Monte S. Angelo, via Cintia, 80126 Naples, Italy 2 Department of Physics, University ‘Federico II’ of Naples, Complesso, Universitario di Monte S. Angelo, via Cintia, 80126 Naples, Italy Abstract The ‘extremely diluted solutions’, anomalous solutions prepared through the iteration of a process of dilution and succussion, have been studied with the aim of obtaining information about the influ- ence of the preparation method on the water structure of the solutions. We measured the heats of mixing of basic solutions with such ‘extremely diluted solutions’, and their electrical conductivity, comparing with the analogous heats of mixing, electrical conductivity of the solvent. We found some relevant exothermic excess heats of mixing, and higher conductivity than those of the un- treated solvent. The heats of mixing and electrical conductivity show a good correlation, underlining a single cause for the behaviour of the extremely diluted solutions. Keywords: calorimetry, conductivity, extremely diluted aqueous solutions Introduction Recent studies on the physico-chemical properties of water put in evidence that the most studied liquid by far, water, still exhibits totally unexpected properties [1–12]. The peculiar characteristics of the water liquid derive from the presence of the hydro- gen bond, that is characterized by a very directional intermolecular potential. Through very precise measurements of the refraction index, it is becoming evident that this liquid, on average, is composed of dynamically interconverting micro- domains of two different structural types [4]. Even a femtosecond mid-infrared pump-probe study suggests that, with respect to orientational dynamics, two distinct molecular species exist in liquid water [5]. Lobyshev and co-workers have shown that the effect of very low concentrations and electromagnetic fields elicit long-scale realignments of the structure of the liq- 1388–6150/2004/ $ 20.00 © 2004 Akadémiai Kiadó, Budapest Akadémiai Kiadó, Budapest Kluwer Academic Publishers, Dordrecht * Author for correspondence: E-mail: elia@chemistry.unina.it