Critical Point Opalescence
Nov. 25th, 2003 07:55 pmHere's something really neat that I just learned. When the partial derivative of the pressure with respect to volume approaches zero, the isothermal compressibility approaches infinity and the fluctuation in density becomes very large. As a result, the scattering of light by this substance also becomes very large, occuring over a very broad range of frequencies. The condition of the vanished partial derivative occurs at the critical point of a substance. As a result, just about any liquid, even transparent or strangely colored ones, will at its critical point assume a milky white appearance. This is called "critical point opalescence."