Optical Properties of Fused Metals. 267 



Owing to lack of knowledge of the electrical conductivity 

 of this metal in the liquid state, it was not possible to utilise 

 the results of these experiments in the earlier paper. 



It appears, however, that the conductivity has been deter- 

 mined by Vassura. The result is quoted, without the precise 

 reference, by W. Williams* in the course of a valuable 

 summary and discussion of the experimental work which has 

 been done in connexion with changes of resistance due to 

 temperature. 



According to Vassura, the ratio of the resistivity just after 

 fusion to that just before is, for tin 2*1, and for cadmium 

 2-3. 



De la Rive has given the corresponding ratios for two 

 other metals, zinc 2*0, and lead 1*9. 



The optical constants are known only for the case of tin, 

 in sodium light. In the notation of the earlier paper, Drude 

 gives 



n=210, x= 2 ' 15 > 

 so that 



i/=2*10, k = 4-o0, ™=9'45, K --v~ = 15'S, 



where v is the index of refraction, and /c the coefficient of 

 optical length. 



According to Vicentini and Omodei's measurements, the 

 density of the liquid metal is 6'988, and its atomic weight 

 being 119'0, the atomic volume of the liquid becomes 17*0. 



For the calculation, from the optical constants, of the 

 effective number of free electrons in an atom, we require 

 the conductivity of the liquid, in absolute measure, at the 

 melting-point, which is 230° C. 



If u denotes the ratio of the resistance at t° C. to that at 

 0° (\, Fleming and De war's measurements for tin give 



nil 



^=•00425 + '000004(H, 

 from which 



(Resistance at 230° C.)/(Resistance at 0° C.) = 2>083, 

 and 



(Resistance at 18° C.)/(Resistance at 0° G.) = l"077. 

 Thus the conductivity just before fusion is 



cr' = 8-28.10- 5 xl-077/2-083 = 4-28. 10" 5 , 



where the ordinary value of the conductivity at 18° C. has 

 been used. 



* Phil. Mag. Mar 1902, p. 515. 



