482 



Dr. Tycho E:son Auren on the 



Table V. shows a survey o£ the values of X. a.k. I have 

 found when examining metals in a solid state. 



Table Y. 



Metal. 



Thickness of 



ineial sheet 



in cm. 



X. a. k. 



Al 



0-06— 0-25 

 0-005 

 001 

 0008 



0-0047 



3-5 

 47-3 



57-0 

 65-4 

 311 



Fe 



m 



Ga 



Sn 





The relative atomic absorption coefficients of the elements 

 that are components of the combinations seen in Table IV. 

 have been calculated and brought together in Table VI. In 

 these calculations, I have started from the values of X.a.k. 

 for oxygen and hydrogen, which are readily obtainable from 

 the determinations of X. m.'k. for Xa010 a , NaCl, and H 2 0. 

 The difference between the values for the former combinations 

 is 2*7; and as this difference depends on 3 atoms of oxygen, 

 the X. a. k. of oxygen will be 0*9. Since X. m. k. of water is 

 1'0, we likewise find the value of X. a. k. of hydrogen to 

 be 0*05. By the intermediary of the values of oxygen and 

 hydrogen, we can then easily find X.a.k. for 01 from HCI, 

 for S from TI 2 S0 4 , for N from HN0 3 , &c, whereupon the 

 values of X. m. k. for the combinations X. a. k. for the other 

 elements have been calculated in the same way. After 

 examining two or more substances, from which the value of 

 X. a. k. for a certain element has been calculated, the especial 

 values as well as the mean value have been given. The table, 

 moreover, gives the so-called atomic numbers, in which case 

 I have used the numbers that of late years have been in 

 common practice (Moseley, Rutherford, &c). 



Apart from the deviations in Co and W, X. a. k. steadily 

 increases along with the increasing atomic weight. 



As to the deviation for W, it certainly depends, as shown 

 before, on selective absorption. In relation to X-rays, Ni 

 appears to occupy the place between Co and Cu, accordingly 

 not the place due to its atomic weight *, and from a chemical 



* Compare Pohl, Die Physik der Rontgenstrahlen ; Moseley, Phil. 

 Mag. xxvi. p. 1031 (1913) j Barkla, Phil. Mag. xiv. p. 408 (1907). 



