MOLECULAR REFRACTION 81 



with regard to refraction the above constant k is to be 

 taken. 



The chief result is that the so-called molecular refraction : 



^ r n 2 i 

 Mk MT-Z 



may be calculated by summation from the values for the 

 components. 



We will again adopt the most radical method, obtaining 

 first the numbers for the elements : the indices refer to the 

 sodium line ] , A is the atomic weight, A the atomic re- 

 fraction : 



Element n A g = A 



Bromine 1.001132 8-46 



Chlorine 1-000773 5'7 8 



Oxygen 1-000272 2-03 



Nitrogen 1.000296 2-20 



Hydrogen 1.000143 1-07 



Carbon (diamond) .... 2-46986 2-15 



The following are some binary compounds : 



n 2 -i 

 Compound n ^7~i \j^ ^^ 



Hydrobromic acid . . 1-000573 8-57 9-53 



Hydrochloric acid . . 1-000447 6-68 6.85 



Water 1-000259 3-86 4' 1 ? 



Nitrous oxide . . . 1-000516 7-69 6.43 



Nitric oxide .... 1.000297 4-43 4-23 



Ammonia 1-000379 5-65 5-41 



Methane 1-000444 6.71 6.43 



Additive relations unmistakably exist, but exactness 

 fails, as almost ever. The deviations, as in the case of the 

 molecular volume are referred to constitutive influences, to 

 determine which organic compounds offer a rich field. It 

 must be borne in mind that owing to varying dispersion, 

 and the failure of attempts to reduce refractive indices for 

 different colours to a common standard, strict additivity 

 is not to be expected ; rather if it existed for any one 



1 Briihl, Zeitschr. f. Phys. Chem. 7. i. 

 F 



