XV.—A Theoretical Atomic Distribution Curve for Liquid Argon at 90° K

The radial distribution of the atoms (or molecules) of liquids, as of solids, can be found from X-ray scattering photographs (Zernike and Prins, 1927; Warren and Gingrich, 1934), and in this way many such distributions have been determined experimentally (Harvey, 1938, 1939; Gingrich, 1940; references in Coulson and Rushbrooke, 1939). The results are generally given as distribution curves showing p(r) or r 2 p(r) as a function of r , where 4πr 2 p(r)dr measures the probability that two arbitrarily selected atoms (or molecules) of the liquid are distant r to r + dr apart. Such distribution curves show a sequence of peaks—for ρ(r) these are usually of diminishing amplitude—and for atomic liquids successive peaks may conveniently be ascribed to successive co-ordination shells (of atoms) about any (arbitrarily selected) central atom. The position and precise shape of the peaks depends, of course, upon the temperature as well as the substance of the liquid.