Royal Society Publishing


The lattice spacings of high-purity iron have been measured accurately between 20 and 1502 degrees C. The results, together with previous low-temperature data, give data between the absolute zero and the melting-point (1534 degrees C). The thermal expansion of the lattice and of bulk metal are in good agreement over the temperature range for which the latter has been studied accurately. At the A$_{2}$ point, there is no discontinuity in the lattice spacing. In contrast to the work of some previous investigators, we have found no observable difference between the coefficients of expansion of the lattice immediately above and below the A$_{2}$ point, and the results suggest that the forces responsible for ferromagnetism do not affect the interatomic distances by more than 1 part in 10000. At the A$_{3}$ point, the $\alpha \rightarrow \gamma $ transformation is accompanied by an increase in the interatomic distance which, when expressed as a percentage change, is slightly less than the decrease in interatomic distance during the $\gamma \rightarrow \delta $ change at the A$_{4}$ point. The change in bond length calculated by the Pauling equation for the change (f.c.c.$\rightleftharpoons $b.c.c.) lies between the observed values for the A$_{3}$ and A$_{4}$ points, and the accuracy of the equation is confirmed.