440 Mr Glasson, Secondary Rontgen Rays from Metallic Salts. 



The value of the absorption coefficient calculated from the 

 initial straight portion is always the same as that obtained for 

 the characteristic radiation from the pure metal. The radiation 

 from the salt thus consists of two parts : 



(i) the homogeneous radiation from the metal, 

 and (ii) mixed with this is a " scattered " radiation due to the 



acid radicle considerably harder than (i). 

 The proportion of this scattered radiation varies with the hard- 

 ness of the bulb. It is generally very small and hence does not 

 evidence itself until the radiation has been very much reduced 

 by screening. This has the effect of cutting off the soft " homo- 

 geneous " radiation much more than the hard " scattered," and 

 hence the latter is shown to better advantage. The smallness of 

 the amount of scattered radiation due to the light atoms is well 

 shown in the case of Ammonium ferrocyanide. In this salt the 

 weight of iron in the molecule is only about one-sixth of the 

 whole. Yet the radiation due to the light atoms does not evi- 

 dence itself until a considerable portion of the beam has been 

 absorbed. 



The information supplied by these curves may be summarized 

 thus : 



(1) The value of the absorption coefficient for the metallic 



radiation is unaffected by its combination with an acid 

 radicle. 



(2) It is independent of the valency of the element in the 



compound. This is well shown by the series of iron 

 compounds FeSOi, Fe304, and FeaOg. 



(3) The element may even occur in the acid radicle itself 



without affecting the value of A,. 



IV. 



In this way it is possible to determine \ for some metals which 

 it is impossible or inconvenient to use in the uncombined state. 

 This has been done in the case of Manganese. The salt used 

 was the sulphate ; the curve is shown in fig. 5. The value of X 

 obtained from the initial part of the curve is 100. This value 

 agrees with that predicted from its atomic weight, using Barkla's 

 curve {Proc. Camb. Phil. Sac. xv. 257). 



I desire to thank Sir J. J. Thomson for his interest in these 

 experiments. 



