Absorption of JRbntgeus Bays by Solutions of Metallic Salts. 421 



weight of the elements of which a salt is composed the greater is the 

 absorption. This effect is most noticeable in the case of bromides and 

 iodides.* In all cases these salts are absorbent, even when the 

 bromine and iodine are combined with the transparent sodium 

 and magnesium. The iodides also are more absorbent than the 

 bromides. 



Now proceeding to the consideration of the absorption produced by 

 salts with other acid radicles, the differences are not so marked, but in 

 all cases the least absorbent salt is the nitrate, the next the chloride, 

 the most absorbent being the sulphate ; this does not agree with the 

 order of increase of the molecular densities, or of the atomic weights 

 of the constituents. It would therefore appear that the absorptive 

 power is not entirely dependent on the atomic weight of the compo- 

 nents of the acid radicle, or on its molecular density ; the order in 

 the first case being (1) nitrates (N = 1'4), (2) sulphates (S = 32), and 

 (3) chlorides (CI = 35-5) • (2) and (3) being nearly equal. While in 

 the second place the order should be : (1) Chlorides (CI = 35 - 5), (2) 

 sulphates (S0 4 = 48) (3) nitrates (N0 3 = 62); while the order 

 actually observed is (1) nitrates, (2) chlorides, (3) sulphates. 



Acetates are slightly less absorbent than chlorides, though the 

 number of salts tried is small ; only four giving results to which 

 weight can be attached, since aluminium and iron were simply powders 

 in suspension and partially precipitated. 



It now remains to be seen if there is any definite connection between 

 the equivalent weight of the bases composing the different salts and 

 their absorptive powers. Their order may be written down as 

 follows : — 



In ascending order of absorption — 



1. Lithium 



2. r Magnesium 



3. < Aluminium .. 



6. \ Potassium 



7. flron 



(7)' 





r Nickel , 



(58-6)' 



(24)" 





Copper 



... (63)" 



(27)"' 



11. 



.Zinc 



.... (65)" 



(23)' 



12. 



Strontium ... 



... (87)" 



(40)" 



13. 





... (137)" 



(39)' 



14. 



Cadmium . . . 



(111-7) 



(56)" 



15. 





.,, (206)" 



(58-6)" 



16. 



Uranium . . . 



... (240)"' 



The metals bracketed together have very nearly /the same absorp- 

 tive power. The order given above does not agree very nearly with 

 the order of increase of equivalent weight ; it agrees more closely, 

 however, with the order of increase of atomic weight. It is to be 

 noticed particularly, that the salts of the alkali metals are less absor- 

 bent than might have been expected from their equivalent weight, also 



* E. Sehrwald, ' Beiblatter ' (1897), p. 64. 



