the Absorption of X-Ruys. 175 



from alifatic and aromatic compounds. If the mean 

 values are computed from the alitatic substances (14 in 

 number) in the first case and from tbe aromatic com- 

 pounds (3 in number) in the second, in which latter case an 

 atom of carbon in toluol and benzyl alcohol is supposed 

 to have the same absorption as in alifatic compounds, 

 then we oet : 





I. 



II. 



III. 



IV. 



Alifatic compounds .. 



0-46 



0-49 



0-50 



0-53 



Aromatic ., 



. 0-47 



0-49 



0-50 



0*53 



Thus we get almost identical values from the two kinds of 

 compounds. A difference which I formerly have found in 

 this respect is entirely elucidated by the fact that, as I pointed 

 out at the time, the values for hydrogen and oxygen were 

 not determined with sufficient accuracy. 



It has seemed to me to be of particular interest to 

 examine how far the absorption of carbon in a solid form 

 has the same magnitude as that of carbon in chemical 

 compounds in liquid state. Therefore I have made several 

 experiments on graphite plates. Here, however, we have 

 the difficulty that completely pure graphite is hardly 

 obtainable. Interspersed extraneous matters, most fre- 

 quently consisting of heavier and hence more strongly 

 absorbing elements, may, even in minute quantities, play 

 an appreciable part in absorption. Professor C. Benedicks 

 has kindly placed Acheson graphite plates at my disposal, 

 which on chemical analysis have proved to contain solely 

 0*2 per cent, of ash substances, chiefly consisting of Fe. 

 On examining this sort of graphite, the following values 

 have been established : — 



I. II. III. IV. 



*C/H ( Acheson graphite) ... 0*59 0-61 062 0*62 



The values thus obtained are markedly higher than those 

 found by examining organic compounds. Owing to tbe 

 included metal particles these values are certainly a little 

 too high, but the stated proportion of ashes does not seem 

 to be so great that the difference can be fully explained by 

 it. It may therefore be possible that carbon in the form 

 of graphite is more strongly absorbing than in the form of 

 organic compounds. Possibly the crystallic structure may 

 have some influence. As, on the other hand, the influence 

 of the included particles cannot with certainty be established, 



