LIQUID

in phonetics, a consonant sound in which the tongue produces a partial closure in the mouth, resulting in a resonant, vowel-like consonant, such as English l and r. Liquids may be either syllabic or nonsyllabic; i.e., they may sometimes, like vowels, act as the sound carrier in a syllable. The r in father or Czech krk neck and the l in rattle are syllabic; the r in rim and the l in lock are nonsyllabic. in physics, one of the three principle states of matter; it is intermediate between gases and crystalline solids. Solids are characterized by low potential energies that result from powerful cohesive forces and bind the constituent molecules together, usually in an orderly pattern. In direct contrast, gases have high potential energies, resulting from weak cohesive forces, that allow free motion and a completely random molecular distribution. A liquid, with its intermediate potential energies and moderate cohesive forces, has neither the orderliness of a crystalline solid nor the randomness of a gas. Its molecules are not capable of unrestricted motion throughout the total volume; rather they are preserved in an orderly array over a few molecular diameters. Other distinguishing features of liquids include an ability to flow under the action of very small shear stresses. Moreover, liquids in contact with their own vapours or air possess a surface tension that, unless opposed by external forces, causes the interface to assume the configuration of minimum area. In the absence of gravity and other forces, the stable form of a mass of liquid is spherical. Surfaces between a liquid and a solid or another immiscible liquid (i.e., one that is incapable of mixing) are also characterized by interfacial tensions, which determine whether the liquid in question will spread on the other material. The electrical properties of liquids are determined by the density of charge carriers. With the exception of liquid metals, molten salts, and solutions of salts in ionizing solvents, the electrical conductivities of liquids are small. In molten salts and solutions of salts the current is carried by the ions of the salt, whereas in liquid metals it is carried by electrons. in physics, one of the three principal states of matter, intermediate between gas and crystalline solid. Additional reading J.N. Murrell and E.A. Boucher, Properties of Liquids and Solutions (1982), is a short introduction to the physics and chemistry of the liquid state. Robert C. Reid, John M. Prausnitz, and Bruce E. Poling, The Properties of Gases and Liquids, 4th ed. (1987), focuses on the vapour-liquid transition, as opposed to the solid-liquid transition, and evaluates and illustrates techniques for estimating and correlating properties of gases and liquids, as well as tabulating the properties of 600 compounds. A. Bondi, Physical Properties of Molecular Crystals, Liquids, and Glasses (1968), focuses on the solid-liquid transition as opposed to the vapour-liquid transition and describes methods for the characterization of higher-molecular-weight liquids. J.S. Rowlinson and F.L. Swinton, Liquids and Liquid Mixtures, 3rd ed. (1982), provides a thorough treatment of the physics of fluids and gives some statistical mechanical theories of the equilibrium properties of simple pure liquids and liquid mixtures; the work also contains a data bibliography and is primarily for research-oriented readers. Dictionary of Organic Compounds, 5th ed., 7 vol. (1982), and annual supplements, is a listing of such properties of organic compounds as chemical formula, density, and melting and boiling points; the work is useful for organic chemists in synthesizing and identifying organic compounds. Gilbert Newton Lewis and Merle Randall, Thermodynamics, 2nd ed., rev. by Kenneth S. Pitzer and Leo Brewer (1961), is a classic text on the thermodynamics of pure substances and solutions, written from the point of view of chemistry. John M. Prausnitz, Ruediger N. Lichtenthaler, and Edmundo Gomes de Azevedo, Molecular Thermodynamics of Fluid-Phase Equilibria, 2nd ed. (1986), employs molecular-thermodynamic concepts useful for engineering and is written from a chemical-engineering point of view. The first three chapters of K.E. Weale, Chemical Reactions at High Pressures (1967), give a description of the behaviour of pure systems and phase equilibria at very high pressures. John M. Prausnitz et al., Computer Calculations for Multicomponent Vapor-Liquid and Liquid-Liquid Equilibria (1980), includes a short, annotated list of literature sources for vapour-liquid and liquid-liquid phase equilibria. Bruce E. Poling