Diffuse Scattering of X-rays from Sylvine

By means of the formulas recently obtained by Compton for monatomic gases and by Jauncey and Harvey for simple cubic crystals $f^{\prime }$ values can be calculated from the observed intensities of the diffuse scattering. The formula for crystals is only valid for the case where the crystal consists of atoms of one kind. Up to the present time the only crystal for which $S$ values were known was rocksalt, but this is a crystal consisting of two kinds of atoms. Sylvine, however, is a crystal consisting of one kind of atom, since the ions ${\mathrm{K}}^{+}$ and ${\mathrm{Cl}}^{-}$ may be considered as argon-like atoms. In the present research $S$ values have been obtained for sylvine at room temperature. If these $S$ values are plotted against $\frac{\left(\frac{sin\phi }{2}\right)}{\lambda }$, an $S$ curve is obtained similar to that obtained by Jauncey and May for rocksalt as described by Jauncey and Harvey. Comparing the $S$ curve for sylvine with Wollan's $S$ curve for argon the two are tangent at $\frac{\left(\frac{sin\phi }{2}\right)}{\lambda }=1.05\mathrm{}$ and beyond this appear to merge. From the formula of Jauncey and Harvey $f^{\prime }$ values for sylvine have been calculated using $F$ values obtained by James and Brindley. Plotting the $f^{\prime }$ values for sylvine and those obtained by Wollan for argon against $\frac{\left(\frac{sin\phi }{2}\right)}{\lambda }$, both sets of points fall on the same curve, the agreement being remarkable. Comparison is also made of these $f^{\prime }$ values with the theoretical $f$ values obtained for a Schroedinger atom by James and Brindley. The agreement is good out to $\frac{\left(\frac{sin\phi }{2}\right)}{\lambda }=1.0\mathrm{}$ but from there on the theoretical $f$ curve falls off too rapidly. It might be expected that the theoretical $f$ curve would fall off too slowly since $f^{\prime }$ is less than $f$. In this region the agreement between theory and experiment could be improved.