Compressibility of the Alkali Halides

Compressibility of eleven alkali halides and its variations with pressure and temperature have been determined by measurements by Bridgman's new method, up to 12,000 atm. for both 30° C and 75° C. The samples were all single simple cubic crystals each grown from the melt in a new way, described elsewhere. The error in the values of the compressibility at zero pressure, ${\kappa }_0$, is probably less than one per cent; in the values for variation with pressure, ${\psi }_0$, and temperature the error may be 5 and 20 per cent respectively. By extrapolation approximate values of ${\kappa }_0$ for absolute zero are found. Periodic relations. Both ${\kappa }_0$ and ${\psi }_0$ when plotted against the alkali ion for a series of salts of the same halogen ion, or vice-versa, show similar behavior. The curves break sharply at the ion similar to argon (K or Cl) the rate of increase suddenly decreasing. This behavior is also shown by the grating space as measured by Davey, and tends to corroborate Bohr's theory of atomic structure according to which there is a discontinuity in atomic formation at argon, additional electrons going into inner shells.