Investigations in the Spectral Region between 20 and 40μ

An apparatus is described which is convenient for studying the optical properties of substances with reststrahlen having wave-lengths from 6 to 150μ. A vibrationless support is described, the essential features of which are copied from the design of R. Müller but the construction is simplified. The transmission of several gases was studied with reststrahlen having wave-lengths 20 to 33μ. S${\mathrm{O}}_2$ shows strong absorption at 20.75μ. The reflectivity of S${\mathrm{O}}_2$ was tested and found to be zero at both 20.75μ and 8.7μ where it has strong absorption bands. Gas absorptions from 20 to 33μ are compared with the Raman indications. Transmissivities and reflectivities of various materials are given for the spectral region 20 to 33μ. $\beta -\mathrm{MgO}$ was found to have a reststrahlen near 23μ. Potassium iodide was found to be transparent to wave-lengths greater than 33μ.