414 Lord Blythswood and Dr. E. W. Marchani. 



absorption were atomic, that is if the absorption of the rays were not 

 produced so much by the nature of the molecule as by the constituents 

 of the molecule, there ought to be some simple relation between the 

 absorbing powers of salts having the same acid radicle. This investi- 

 gation, however, was originally suggested with a view to finding out 

 whether the very great difference in the transparency of individuals to 

 Kontgen rays might not be caused by an excess of some salt in the 

 composition of the blood or muscular tissue.* Some results have been 

 obtained by different experimenters, the most exhaustive treatment of 

 the subject up to the present having been given by Dr. Gladstone and 

 Mr. Hibbert (B.A. Eeports, Section B, 1896, 1897, 1898).f They 

 found that the physical condition of the absorbing substance (whether 

 solid or liquid) .produced no very marked differences, also that the 

 absorption of a mixture of salts was the same as that of the double salt, 

 in the same state of division, and that the change in atomicity of the 

 absorbing substance produced no appreciable effect, also that the total 

 absorption produced by a solution was the sum of the absorptions of 

 the salt and its solvent. 



They also found that the absorptive power depended on the atomic 

 weight and not on the density or combining proportions ; using an 

 aluminium stepped scale they found that the absorption appeared to 

 increase logarithmically with the thickness of aluminium traversed. 

 The same experimenters have also examined the absorptive power of 

 various metals and metallic salts, and have compared that of different 

 acid radicles. Before, however, their results were published the 

 present investigation was taken up, and the results obtained appear to 

 be of considerable interest. Similar results have been obtained by 

 several others, | but all are included in the more exhaustive work of 

 Dr. Gladstone and Mr. Hibbert. 



The great difficulty found in the investigation was the obtaining of 

 quantitative results, as, although it is a comparatively simple matter to 

 obtain approximate qualitative results, it is much more difficult to 

 obtain even approximately accurate quantitative values. The only 

 method which appeared to offer much prospect of success was a photo- 

 graphic one, and all the values given below have been obtained photo- 

 graphically. 



The first method adopted was to place two cells made of thin glass 

 in front of two holes cut in a thick lead sheet, one cell being filled with 

 water and the other with the solution to be tested ; the photographic 



* Cf. Bouchard, ' Coinptes Eendus,' vol. 123, pp. 967 and 1042. 

 t ' Chemical News,' Nov. 13, 1896, and Oct. 21, 1898. 



X Meslans, ' Comptes Rendus,' vol. 122, p. 307 ; Bleunard and Lablesse, ibid., 

 vol. 122, pp. 527 and 723 ; Van Aubel, 'Jour, de Physique,' rol 5, p. 511; Novak 

 and Sulc, ' Beiblatter,' vol. 20, part 5, p. 414 ; F. Re, ' Elettricita ' (Milan), pp. 

 261-264 (1898). 



