Absorption of Rontgeris Rays by Solutions of Metallic Salts. 427 



in the intensity of the photographic image, according to the thickness 

 of the solution traversed, appearing to be much less than with rays of 

 greater penetrative power, although, as stated above, the thickness of 

 the solution necessary to produce the same amount of absorption as 

 20 mm. of water was constant within limits of experimental error. * 

 This agrees with the observation of M. Buguet (loc. cit.). The 

 values of A. for the different solutions have not therefore been calcu- 

 lated. 



The value of /x for the apparatus used would (from the comparatively 

 close agreement with theory of the above numbers) seem to be 

 negligible. 



The results given above show that the logarithmic law is at any rate 

 approximately true. 



Conclusions. 



1. The absorption produced by normal aqueous solutions of metallic 



salts having the same acid radicle, increases with increase of 

 atomic weight of the base. 



2. Metals belonging to the alkali group are not very absorbent, 



neither are those belonging to the calcium, strontium, and 

 barium group, their atomic weight being taken into con- 

 sideration. 



3. Bromides and iodides of the metals are all highly absorbent. 



4. With the three common acids, the order of increasing absorptive 



power is nitrate, chloride, sulphate. 



5. The absorption produced by a salt is dependent mainly on the 



atomic weight of its constituents. 



* Considering this statement in the light of the known facts with regard to the 

 photography of the bones of the hand, it will be seen that facts are not in contra- 

 diction to the conclusions drawn from these experiments. With rays of low pene- 

 trative power, the whole hand appears dark though the screen appears light 

 (assuming \ large for the flesh and much larger for the bones), the reason being 

 that both the flesh and bones absorb nearly all the rays. Assume, for example, that 

 for this penetrative power the flesh allows only 1/100 of the light to pass and the 

 bones 1/1000. Now, using rays of greater penetrative power we may assume that 

 the flesh will allow l/10th of the light to pass while the bones will only allow 

 1/1 00th to pass. The bones will now be faintly visible. Pushing the penetrative 

 power still further, assume that the flesh now allows half of the light to pass, the 

 bones will allow only l/20th, and will be very sharply defined. With still further 

 exhaustion of the tube the flesh may now be assumed to allow 9/10ths of the light 

 to pass, while the bones still only allow 1/llth ; and, as is known, at this stage the 

 bones themselves begin to appear transparent. 



At the same time it is not assumed that the ratio of the absorption for the 

 different salts does remain constant throughout this very wide range, but that the 

 fact that the ratio of the absorptions appears to remain constant through a limited 

 range while the actual absorption may differ appreciably through this range, is not 

 in contradiction to other observations. 



