390 



TABLE 498. 

 X-RAY SPECTRA AND ATOMIC NUMBERS- 



Kaye has shown that an element excited by sufficiently rapid cathode rays emits Rontgen rays characteristic of 

 that substance. These were analyzed and the wave-lengths determined by Moseley (Phil. Mag. 27, 703, 1914), using 

 a crystal of potassium ferrocyanide as a grating. He noted the K series, showing two lines, and the L series with several. 

 He found that every element from Al to Au was characterized by integer N, which determines its X-ray spectrum; 

 N is identified with the number of positive units associated with its atomic nucleus. The order of these atomic num- 

 bers (AT) is that of the atomic weights, except where the latter disagrees with the order of the chemical properties. 

 Known elements now correspond with all the numbers between i and 92 except 6. There are here six possible elements 

 still to be discovered (atomic nos. 43, 61, 72, 75, 85). 



The frequency of any line in an X-ray spectrum is approximately proportional to A (N ft) 2 , where A and ft are 

 constants. All X-ray spectra of each series are similar in structure, differing only in wave-lengths. Q K = fr/fw); 

 Q^ = (r/,ftto) where r is the frequency of the a line and vo the fundamental Rydberg frequency. The atomic number 

 for the K series = Q K + i and for the L series, Q L + 7-4 approximately, vo = 3.29 X lo 1 * 



Moseley's work has been extended, and the following tables indicate the present (1919) knowledge of the X-ray 

 spectra. 



(a) K SERIES (WAVE-LENGTHS, X X io 8 CM). 



SMITHSONIAN TABLES. 



