Absorption of Hard X-Rays in the Lightest Elements. 743 

 " Table VI. 



I. II. in. iv. v. yi. 



Ktxm * 0-504 0-532 0-547 0-560 0-572 0-575 



K C H 2 



6/e H , H0 0-408 0-486 0-528 0558 0"576 0-588 



A 0-096 0-046 0-019 0'002 -0-004 -0-013 



ATjy/HoO " °" 663 ° 675 °' 674 ° 683 °' 684 °' 685 



7a: H /h o °' 476 °" 567 °' 616 °" 651 °' 672 °' 686 



A 0-187 0-108 0-058 0-032 0*012 -0-001 



KOK.0 °' 874 °' 838 °' 824 °' 814 °' 808 °' 804 



8/ch.HoO °" 544 °' 648 °" 704 °' 744 °' 768 °' 784 



A 0-330 0190 0-120 0070 0040 0-020 



8 «h/h 2 o is considerably greater, which shows that true 

 absorption is proportionally greater in than in lighter 

 elements. If we compare the values of tf a /H. 2 o for the three 

 elements with one another, we find that while the values for 

 C and N are continually increasing towards a maximum, they 

 are, on the contrary, decreasing for and approaching to a 

 minimum. Indeed, according to formula 3 this must be the 

 case, if the term ka\ b is proportionally much greater in the 

 case of than for the other two elements. As I have 

 previously found, it also results from these experiments that 

 true absorption is increasing much more rapidly at O than 

 with the preceding elements. I have assumed, as a possible 

 explanation of this increase of absorption, the suggestion 

 that there is a re-grouping taking place in the electrons, in so 

 far as four electrons are concentrating nearer to the nucleus 

 and are forming an inner region, whereas the remaining* 

 four electrons form a group of outer electrons (valence 

 electrons). The suggestion that the number of the outer 

 electrons is likely to be four at O is supported by the fact 

 that of all chemical compounds hitherto known of which 

 this element is a constituent, oxygen does not appear to be 

 capable of a greater number of valences than four. 



Nobel Institution for Physical Chemistry, 

 Stockholm, February 1920. 



