406 



Dr. J. H. Gladstone. 



[June 16, 



the line A, of about 22 for each pair of doubly-linked carbon-atoms. 

 Assuming this to be due to a different value for carbon, we obtain a 

 refraction equivalent of S'O + l'l, i.e., 6*1. In all such cases there is 

 a great increase of dispersion ; this increase, however, is not always 

 the same. In the allyl compounds, whether determined by Briihl, 

 Kanonnikoff, or myself, it is uniformly very close to 0*5. In the 

 defines it is the same. In the whole of the aromatic series it is at 

 least - 8. Coincident therefore with the higher refraction equivalent 

 for carbon, we have two dispersion equivalents of about 0'26 + 0*25, 

 and 0-26 + 0-40, i.e., 0-51 and 0*66. 



It must remain for future consideration, whether there may not be 

 an intermediate refraction equivalent, corresponding to the dispersion 

 equivalent of 0'51. 



On the appearance of Briihl's papers in 1880, I ventured to suggest 

 that there was a still higher refraction equivalent for carbon, in those 

 cases in which it " has all four of its units of atomicity satisfied by 

 other carbon-atoms, each of which has the higher value of 6*0 or 6*1," 

 as in naphthalene or pyrene. This view has been, and is, the 

 subject of controversy, but on turning to the dispersion equivalents of 

 these bodies, they are found to be always enormously high, far higher 

 than can be accounted for by the figures with which we have hitherto 

 been dealing. 



Oxygen. — It has been established by Briihl, that in the case of 

 aldehydes and ketones, oxygen has a refraction equivalent of 3'4. As 

 these have the general formula C„H 2re O, and the dispersion of CH 2 is 

 known, it is very easy to determine the dispersion equivalent of the 

 oxygen. Various determinations of these bodies give a fairly uniform 

 result; viz., 0*18 for H— A. 



In the case of the alcohols, the oxygen has a refraction equivalent 

 of only 2*8. Comparing the dispersion equivalents of the alcohols of 

 different atomicities in the published lists, the mean value for oxygen 

 in this condition comes out at about 0-10. Nevertheless, in the 

 organic acids and compound ethers, the value of the two oxygens 

 together seems rarely if ever to exceed 0'24. 



Chlorine. — Our lists also give us the means of determining the 

 value of chlorine in organic substances of the fatty acid series. As 

 reckoned from such substances as chloroform, chloral, ethylene, and 

 ethylidine chloride, and bichloride of chlorethylene, the dispersion 

 equivalent of this halogen appears to be 0*50, though in the simple 

 chlorides of the compound radicles it appears to be a little less. 



Bromine. — The dispersion equivalent of bromine varies in a similar 

 way to that of chlorine. As deduced from bromoform and the 

 di bromides of the olefines, it is 1*22 ; but in the bromide of ethyl it is 

 lower. 



Iodine. — The dispersion equivalent of iodine in di-iodide of me- 



