The Crystal Structure of Sodium Nitrate
SYNopsIs. The crystal structure of sodium nitrate has been determined from a study of the Laue pho&graphs obtained by passing X-rays through crystal sections. The method of interpretation is similar to that used by Nishikawa in studying spinel. The unit rhombohedron of sodium nitrate is a body-centered structure containing two molecules of NaNO&. The marshalling of the atoms in the crystal as a whole resembles that within a crystal of sodium chloride with NO3 groups replacing the chlorine atoms
... the chlorine atoms of NaCl. EASUREMENTS of the reflection spectra from the (too) and (III) faces of sodium nitrate have been made by W. L. Bragg. ' Because of the close crystallographic relationship between calcite and sodium nitrate and because of their similar spectra it was concluded that the atoms in sodium nitrate are arranged in the same fashion as are the atoms in the more thoroughly studied calcium carbonate. If this arrangement for the atoms in sodium nitrate is the correct one, then univalent sodium replaces divalent calcium, and trior quinquivalent nitrogen replaces quadrivalent carbon without changes in the crystal structure. The inevitable conclusion is that in these two compounds there is no peculiar connection between the valencies of the atoms concerned and their arrangemerit in space. This conclusion is of such great importance that it seemed desirable to assure its truth by a more detailed study of the structure of sodium nitrate. Consequently a determination of the crystal structure was made from a study of the Laue patterns obtained by passing rays through sections of sodium nitrate cut parallel to the (zoo) and the (r xz) faces. The method of interpretation is a modification of that used by Nishikawa' in studying spinel. THE SPECIMENS. The crystals used in these experiments were obtained by the slow evaporation over sulphuric acid of a solution of sodium nitrate. The specimens used were perfect rhombohedra about one centimeter on a side.