Light at certain Metal-Liquid Surfaces. 



233 



so calculated and those given by the direct refraction 

 methods (w ). In the following Table are given the values 



of 



and ?? , as calculated from the experimental results. 



It includes all the observations on record *. 



Gold in Water . 



„ CS 2 .... 



Silver in Water 



„ Terpentine 



I ,. CC1 4 



Copper in Water 



„ Alcohol .. 



,, Cassia Oil 



cs 2 



Mercury in Water .. 

 Alcohol .. 



HC1 (dilute) 



., (cone.) 



Na 2 S 2 3 (cone.) ... 

 „ (sup. sat.) 



Petroleum 



Chloroform 



Olive Oil 



Turpentine 



CS 2 



1-33 

 1-64 

 1-34 

 1-33 

 1-34 

 1-47 

 1-46 

 1-33 

 1-37 

 1-61 

 1-63 

 1-33 

 1-36 

 1-39 

 1-39 

 1-42 

 1-43 

 144 

 1-44 

 1-47 

 1-47 

 1-47 

 1-63 

 1G3 



Observer. 



Conroy. 



Quincke. 



Conroy. 



Sissingh. 



Quincke. 



Conroy. 



Drude. 



Des Coudres. 



Now it is impossible to ascribe these discrepancies in 

 every case to films of surface contamination ; for they occur 

 for those metals (notably copper and mercury) for which 

 entirely satisfactory results in air have been obtained, and 

 under circumstances apparently precluding the formation 

 of any chemical film. Hence, as we have seen that it is 

 highly probable that a perfectly clean metal possesses no 

 appreciable transition layer when in contact with air, it is 

 only possible to ascribe these discrepancies to a transition 

 layer due to the liquid. Now, an inspection of the above 

 Table shows that the index calculated from the reflexion 

 from the metal is in all but four cases less than that deduced 

 by the direct refraction methods. On the theory as developed 



* The values are taken from a paper by Drude, Wied. Ann. xxxix. 1891, 

 p. 539. The calculations have been verified, except in the case of the 

 experiments of Sissingh and Des Coudres, to whose original papers I 

 have not had access. 



