Results of measurements of the mass attenuation coefficients (μen/ρ) and the dispersion corrections f’ and f” have been given in two recent papers. The data cited in these papers were gained using both a conventional XRF spectrometer and a multiple reflection double crystal spectrometer based on the Bonse-Hart low angle scattering camera. Both of these techniques have deficiencies which limit their usefulness in operation. The XRF technique has been shown to become inaccurate for thick specimens. The multiple reflection spectrometer experiences alignment and stability problems, because, for each wavelength, three different axes must be adjusted. Since the angle of acceptance of the grooved multiply-reflecting elements is less than 10 seconds of arc, any misalignment of one element of the spectrometer with respect to the other causes large variations in the intensity of the beam transmitted through the spectrometer.