of Molecular Refraction and Dispersion, 



207 



he published another paper giving fresh and additional values 

 for alums containing these metals *. 



For indium the available data are derived from rubidium 

 and caesium indium alums, and for gallium from no fewer 

 than five compounds, viz., potassium, rubidium, caesium, 

 thallium, and ammonium gallium alums. Calculated from 

 these data, I find as mean values for the atomic refraction of 

 these two metals the following : — 



Metal. 



Atomic Weight. | j^f^L. 



A 



Indium 



113-4 0-121 

 69-9 0166 



13-7 



11-6 



i 



Gallium 





These no doubt are nearer the truth then the higher figures 

 previously given, though they must still be looked upon as 

 only approximate. In regard to the atomic dispersion of 

 these metals, the new observations quite confirm the previous 

 remark that the order is " iron far the highest, chromium, 

 indium, gallium, and aluminium lowest." 



III. SULPHUK. 



In the following Table is given the atomic refraction of 





sulphur, either 



uncombined, or in very simple 



combination : — 



Condition. 



A. 



C, or 

 " red." 



D, or 

 " white." 



F. 



G or y. 



H. 



Solid 



15 : 98 



15 : 5 



15-8 



15-7 



mi" 



15-7 



16-05 

 15-8 

 15-9 

 16-35 



16-0 

 16-47 



160 

 16 3 

 16-0 

 161 



16-7 



17-05 



17-3 

 17-7 



18-4 



Liquid 





In solution 



From CS, 



„ ci/s 



» C1 2 S 2 



„ Br 2 S._> 



iSulphur in the solid condition is deduced from the observa- 

 tions of Descloiseaux and other physicists; but as the crystals 

 of sulphur give three different indices of refraction for the 

 same ray, the arithmetical mean of these three indices has 

 been simply taken as the basis of calculation. 



Sulphur in a liquid condition is from the observations of 



Archives Sc. Ph. fy N. Geneve, xiv. p. 96. 



