Abstract
The phase transitions from close packed to distorted structures occurring in Cd-Mg and In-Tl alloys are discussed. The authors document and apply the nearest neighbour theory derived in a previous paper by Finnis and Heine (see ibid., vol.4, no.7, 960, 1974) to explain the nature of the distorted phases and the behaviour of the elastic constants at the transitions. They identify these as examples of the R and F types of transition respectively, defined previously.