A crystal spectrograph for measuring absorption coefficients of soft x-rays in gases has been constructed, and with it absorption coefficients of air, argon and oxygen have been measured for spectral lines of wave-lengths 1.537, 2.284, 4.145 and 6.973A. Absorption coefficients in the regions immediately adjacent to the $K$ absorption limit of argon have been measured with general radiation. No departure from the ordinary absorption law greater than experimental error was found in these regions. The magnitude of the $K$ absorption discontinuity of argon was measured by a method which is not dependent upon the extrapolation of curves to the absorption limit, and also by a method which is independent of the absolute magnitude of the absorption coefficients on either side of the absorption limit.

• Received 16 October 1931

DOI:https://doi.org/10.1103/PhysRev.38.1932