Dispersion in Relation to the Electron Theory. 475 



refraction. Taking propionic acid, for which P = 17*46„ 

 we have 



17-46 = 2(CC) + 5(Cfl) + (CO) + (OH) + 2(C0) + 3C + 6H + 20 

 = -829 + 6-765 + -574 + 1-173 +S(CO) + 3'735 + -522 + 2-026 

 whence S(CO) = 1*836. 



The additive relations between the refractive powers or 

 the magnetic rotations deduced by the methods of Landolt, 

 Briihl, and Perkin, rest solely on the constancy of the differ- 

 ence introduced by the addition of the group — CH 2 — in 

 different series of homologous compounds. But we must 

 note it is perfectly arbitrary whether the summation shall be 

 referred to the atoms alone, as in the usual theory, or to the 

 valency linkages alone*, or to the two combined as in the 

 present theory. For this theory it may be claimed (1) that 

 it contains internal evidence of its truth, (2) the values 

 obtained admit of a more rational interpretation than those 

 of the ''atomic " method, (3) it correlates the phenomena of 

 magnetic rotation and refraction. 



The test referred to in (1) is provided by the alcohols. 

 The value of the (OH) linkage may be determined from the 

 molecular rotation, or independently from the refraction. 

 For the latter, taking propyl alcohol, we have P = 17*46, 

 and therefore 



17-46 = 2(CC) + 7(CH)+(CO) + fOH) + 3C + 8H + 

 = 16-319 + OH; 

 whence OH = 1-141. 



The value of OH deduced from the magnetic rotation of 

 propyl alcohol is 1*173, a sufficiently close agreement. The 

 mean value of OH deduced from the refraction of six 

 alcohols is 1*136. 



With regard to (2) it may be remarked that the small 

 values of the (CO) and (CO) linkages indicate higher 

 frequencies and therefore stronger controlling forces on the 

 electrons, than in the (CH) and (OH) linkages. This result 

 may reasonably be associated with the more easily replaceable 

 character of the H atoms in the latter. Further, the atomic 

 value for H is very small (-087), which accords with its 



* In terms of the linkages alone I find the following values for the 

 components of the molecular refraction for the H^ line : — 



(CH)=l-683, (CC)=l-249, (CO) =1-483, (OH) = l*627, (C = O) = 3-404. 

 Thus for ethyl alcohol: P a = 5(CH) + (CC)+(CO) + (OH) 



= 12-78. (Observed value 12-71.) 



