2 Messrs. J. H. &, Gr. Gladstone on the Refraction and 



These figures give the following molecular refraction, i. e. 

 the refractive index minus unity, divided by the density and 



multiplied by the atomic weight, ( , P), which is usually 

 indicated now by R: — * 



j Formula. 



E A . 



R c . 



Ed- 



R F . 



R G . 



K H . 



Fluorbenzeue . . . 



C 6 H 5 F 



4292 



4333 



43-70 



44-68 



45-61 



46-40 



Chlorobenzene ... 



C 6 H 5 C1 



52-29 



52-79 



53-28 



54-52 



55-69 



56-75 



Broniobenzene ... 



C 6 H 5 Br 



57-52 



57-90 



58-65 



60-11 



61-48 



62-69 



Ioclobenzene 



6 H 5 I 



67-49 



68-27 



6908 



71-05 



72-87 



74-68 | 



Before dealing with these observations, it may be well to 

 compare them with figures obtained from totally different 

 specimens of broniobenzene and iodobenzene, which have not 

 yet been published. The observations on broniobenzene were 

 part of a series made some years ago with a view of testing 

 the law that the specific refractive energy of a liquid is very 

 little, if at all, altered by changes of temperature. The 

 method adopted was that of determining the refractive index 

 and density of the same specimen on a cold winter's day and 

 on summer days, the liquid being carefully preserved in a 

 well-stoppered bottle between the observations. The iodo- 

 benzene was a specimen prepared by Dr. Perkin. 





Temp. 

 (J. 



Density. 



A*A- 



*D- 



hr 



fi K . 



Broniobenzene ... 



o 



1-5 



1-51905 



1-5581 









1-6080 



,, ... 



23-3 



1-49225 



1-5476 



1-5586 





1-5971 



„ 



300 



1-4833 



1-5442 







1-5926 



Iodobenzene 



7-0 



1-8537 



1-6129 



1-6275 



1-6450 



1-6777 



These, reduced to the molecular refraction, are as follows : — 



