The Grating Space of Calcite and Rock Salt

Grating spaces of calcite and rock salt are recalculated using the new values for the crystal densities obtained by DeFoe and Compton, and come out for calcite 3.0291±.0010A and for rock salt, 2.8147±.0009A at 20°C. The values for each degree from 15° to 25° are given in a table. These values are slightly greater than those usually given. The remaining uncertainty is due chiefly to that in Avogadro's number. The ratio $\frac{D\left(\mathrm{CaC}{\mathrm{O}}_3\right)}{D\left(\mathrm{NaCl}\right)}$ comes out 1.0762±.0002(18°C) which agrees satisfactorily with Siegbahn's value, 1.0764. The uncertainty in this value is chiefly associated with the molecular weights.