Empirical regularities in the behaviour of the critical constants of fluidalkali metals

We report new measurements of the densities of the coexisting liquid and va pour phases of the alkali metals K and Na. Comparison of the coexistence cu rve of K with those of Cs and Rb in reduced form shows that the alkali meta ls behave very similarly close to the critical temperatures. The experiment al values of the critical constants T-c, p(c) and V-c comply with the empir ical relationships TcVcn = constant and p = constant. T-c(m) with n = 0.31 and m = 3.9.