_The Scientific American_ (September, 1924) published an abstract of a paper read before the _Deutschen Bunsen-Gesellschaft_, in which Dr. D. Coster showed that “the relations between the X-ray spectra of the different elements are so simple that, in some respects, they are more useful for purposes of chemical analysis than ordinary luminous spectra. An important advantage is the fact that the X-ray spectrum of an element is quite independent of the nature of the compound containing it. It is easy to detect the presence in a mixture of which not more than one milligram is available. Certain precautions are necessary in examining the X-ray spectra; although the number of lines for each element is comparatively limited, recent observations have shown the existence of a number of weaker lines; in addition to this, with the high voltages now generally used, not only the spectrum of the first order, but also those of higher orders appear. Slight impurities in the material of the anticathode, and in the subject under examination, also give their lines, so that there are often various possibilities to be considered before a given line can be explained. Not only the wave length, but also the typical appearance of the suspected lines must be considered, as well as their relative intensity. By measuring photometrically the intensity of the spectral lines it is possible, in some cases, to obtain a quantitative estimate of the amount of an element present in a mixture.” Another method of rapid analysis of material in the laboratory by the use of X-rays in a much shorter time than that required by the older chemical methods is that devised by Professor Urbain, of the Minero-Chemical Laboratory at the Sorbonne, with the assistance of Eugene Delaunay. Mr. Delaunay, who did the actual work of testing the new X-ray method, says there is no risk of error. By employment of X-rays the scientist is now able to ascertain the arrangement of the atoms and molecules within the crystal “network” (structure—or “space lattice” of the crystal).[1] The results are obtained from the study of the reflection and refraction of the rays by the crystals, or, more precisely, the successive rows of molecules in the crystal. These act toward the extremely short X-rays in the same way as a grating spectroscope does to ordinary light-rays.