The melting temperatures of H₂, D₂; N₂ and CH₄ are analysed. The computed results are in very good agreement with the experimental data in each solid. Further, the analysis indicates the presence of the melting maximum in these solids.

In the present paper, a model has been used to develop a simple relation to study the pressure dependence of self-diffusion in solids and liquids that has two adjustable parameters. The computation done in each substance is found to be in very good agreement with the experimental data. It is interesting to note that the present relation is also capable of giving the activation volume in solids and liquids. The activation volume computed in the solids is found to be in very good agreement with the data available.