﻿Absorption of the /3 Ray s from Uranium. 

 Absorption of the Elements, 



385 



Over thirty elements have now been determined, with the 



results shown in the following table : — 



Substance. 



At. Wt. 



X/ P . 



Substance. 



At. Wt. 



X/P- 





11 



12 



23 



24-4 



27 



28 



31 



32 



39 



40 



48 



52 



56 



59 



633 



65-5 



465 



4-4 



495 



51 



526 



5 '5 



61 



66 



653 



647 



62 



625 



64 



648 



6-8 



695 



Arsenic 



75 



79 



87-5 



907 

 106 

 108 

 118 

 120 

 126 

 126 

 137 

 195 

 197 

 207 

 240 



8-2 



8-65 



8-5 



8-3 



8-0 



83 



9-46 



9-8 



108 



108 

 8-8 

 94 

 9-5 



10-8 



101 



Carbon 



Sodium 



Selenium 



[Strontium] 



Zirconium 



Magnesium 



Aluminium 



Silicon 





Silver 



Phosphorus 



Sulphur 



Tin 



Antimony 



Tellurium 





Iodine 



Titanium 



Chromium 



Iron 



Cobalt 



[Barium] 



Platinum 



Gold 



Lead 





[Uranium] 



Zinc 





The whole of the above values were obtained from the 

 elements themselves, except in the case of strontium, barium, 

 and uranium, values for which were calculated from the 

 absorption of their oxides, in a way which will be subsequently 

 described. A comparison of these results with those of 

 Rutherford shows on the whole a satisfactory agreement, 

 except in the case of tin. The discrepancy here is probably 

 due to the fact that the absorption for tin, as explained above, 

 does not follow a simple exponential law. A calculation of 

 X from the first few points on the curve for tinfoil gives a 

 value very near that of Rutherford. 



If now we plot the values of \/p given in the above table 

 against the atomic weights, we obtain the curve shown in fig. 3 

 (p. 386). This curve presents several points of interest. It 

 will be seen at once that the elements arrange themselves very 

 definitely along a series of' similar curves. Moreover, these 

 curves correspond closely in extent with the divisions of the 

 Periodic Classification of Chemistry. Boron and carbon 

 stand alone as the only representatives of the first short 

 period. The second short period is represented by a distinct 

 portion of the curve rising from sodium to sulphur. Potassium, 

 the first member of the first long chemical period, is the first 

 point on a fresh portion of the curve, which extends through 

 the whole of the first long period to selenium. Another dis- 

 tinct section of the curve runs from strontium to iodine, thus 



Phil. Mag. S. 6. Vol. 12. No. 70. Oct. 1906. 2 C 



