151 



we shall only discuss here some of their results, in so far as they 

 are important for testing our general conclusions as to the structure 

 of the regular, unlimited, molecular systems to wich we were led 

 hitherto in this chapter. 



24. Every metal used in the X-ray-bulb as anticathode is 

 stimulated to the emission of X-rays characteristic for that metal l ) 

 Some of them give spectra of very few lines, most of them such of 

 a somewhat more complicated structure (doublets), although the 

 most intensive lines are also in this case rather small in number, 

 and belong to only two or three different series, which are commonly 

 distinguished as K- L-, and M-series. 



Within a certain range of the spectrum, two or three of the most 

 intense lines may be used for the experiments to be described further 

 on, so that these are carried out with a source of radiation which, 

 although not monochromatic in the true sense of the word, gives 

 results which ordinarily are easily controlled and interpreted. 



Such rather simple X-ray-spectra can be obtained by means of 

 anticathodes made from palladium, rhodium, tungsten, or platinum. 

 The rhodium-a.ntica.ihode chiefly emits rays with the wave-lengths : 

 0,537.10- 8 cm.; 0,545. 1Q- 8 cm.; 0,614.10- 8 cm. and 0,619.10~ 8 

 cm., -- the latter being much more intense than the former. The 

 palladium-anticathode gives radiations of 0,583. 10~ 8 and 0,589. 10 

 cm., and of 0,516.10 8 and 0,503.10 8 cm., while in another series 

 there is again a wave-length of 4,622.10 8 cm. Tungsten emits a 



is ground in a mortar and brought into the form of a finely divided powder. This is 

 then shaped into a thin cylindrical rod, and fixed in a position parallel to the axis of 

 a cylindrical photographic camera, provided with a sensitive film. The rod is exposed 

 to monochromatic R on t gen-radiation, entering through a thin aluminium-window 

 in the side of the camera, and propagating in a direction perpendicular to the axis 

 of the cylindrical film. The crystal-particles, orientated in all directions of space, 

 reflect the incident rays in such a way that the dispersed rays are situated on the 

 surface of circular cones, each of those corresponding to a special set of parallel 

 net-planes in the minute crystal-particles. The intersections of these conical surfaces 

 with the film produce a series of curves, the distance and intensities of which 

 are definite functions of the characteristic molecular distances of each set of net- 

 planes. The calculation of the results is rather complicated, but exhaustively treated 

 by Runge, Johnsen, etc. 



!) W. H. and W. L. Bragg, Proceed. Roy. Soc. London, 88, A, 428, (1913); 

 H. G. J. Moseley and C. G. Darwin, Phil. Mag., (6), 26, 210, (1913); H. G. J. 

 Moseley, ibid. (6), 26, 1024, (1913); (6), 27, 703, (1914); E.Wagner, Phys. Zeits., 

 18, 405, 432, 461, 488, (1917); M. Siegbahn, and W. Stenstrom, ibid., 18, 

 547, (1917). 



