472 Mr. S. S. Richardson on Magnetic Rotary 



The magnetic rotation is usually measured for the sodium 

 line, and the molecular rotation generally recorded is not 

 the absolute molecular rotation but the ratio of this quantity 

 to the corresponding quantity for water. Calling the ratio 

 R w and substituting the usual numerical values of the 

 constant?, we have 



R» ()l2 ^ 2j2 *43-748 = {P 1 2 + P 2 2 + ... + P/}, • (2) 



in which the molecular rotation is expressed in terms of the 

 molecular refraction components. 



According to the theory put forward above, only the 

 electrons of class II. (a) or II. (b) influence the dispersion 

 and magnetic rotation. In general, where the resonators 

 II. (b) are not operative, the number of terms in the sum- 

 mation will depend on the number of bonds only, and the value 

 of P for each bond may be calculated. Using the notation 

 (CC), (OH), to denote the value of P for the electron con- 

 cerned in each linkage respectively, we may deduce the 

 numerical values as follows. 



Taking the two hydrocarbons pentane and hexane^ for 

 example, we have by experiment, 



For hexane R w = 6*670, ?? D = 1*3754 ; 



For pentane R„, = 5*6h8, ?? D = 1*3581. 



Substituting these values in (2), 



26*50 = 5(CC) 2 + 14(CH) 2 (hexane), 



22-6Q5 = 4(CC) 2 + 12(CH) 2 (pentane), 

 whence 



(CH) 2 = 1*831, (OC) 2 =--*172. 



On account of the approximate constancy of: the differences 

 for a CH 2 group, only two independent equations can be 

 obtained from a homologous series. Hence we cannot 

 obtain evidence from equation (2) of the null effect of 

 electrons of classes III. and IV., and for the present must 

 rely on the considerations already given. Numerical con- 

 firmation will be obtained when we come to the calculation 

 of refraction for the alcohols. 



For the value of the CO linkage we may consider one of 

 the ethers. Selecting ethyl ether, 



R w = 4-800, n D = 1*3566, 



19*315 = 2(CC) 2 + 10(CH) 2 + 2(CO) 2 , 



whence (CO) 2 = *3305. 



