Systematic experiments, using a sensitive dilatometric technique, have been carried out on the transformation temperatures of two samples of metallic tin and of a number of dilute tin-rich alloys. Vulcan tin (99$\cdot $997% pure-major impurity iron) transforms in the temperature range 9$\cdot $9 to 10$\cdot $8 degrees C, while Pass-S tin (also 99$\cdot $997% pure-major impurity lead) transforms in the range 13$\cdot $0 to 13$\cdot $6 degrees C. The transformation temperature observed for a given sample is higher the greater its 'activity' (as measured by the time necessary to secure 40% transformation from grey tin to white tin at 30 degrees C), suggesting that the observed change point is a function of the strain energy of the white tin formed. Additions of lead, bismuth, antimony and tellurium in the range 0$\cdot $001 to 0$\cdot $005 at.% raise the apparent transformation temperature of Vulcan tin, while similar quantities of zinc and aluminium have little effect. Substantial additions of zinc, aluminium, tellurium and germanium lower the observed transformation temperature of Vulcan tin. The results are discussed and it is suggested that those elements which raise the transformation temperature do so by increasing the degree to which strain energy may be retained in the white tin formed by the transformation.