of Refraction of the Metals. 



15 



No. 



8. 



i 



a. 



it. 



Red. 



White. Blue. 



Eed. 



White. 



Blue. 



1 



o 



40-36 

 12-35 



+93-71 



+49-26 



+93-02 +76-80 

 +47-23 +42-04 



3-31 

 499 



3-29 



4-82 



2-90 

 4-40 



The differences in the values of n in these two prisms far 

 exceed the errors of observation; no doubt the percentage of 

 oxide is greater in the second prism than in the first. It is 

 worthy of remark that there is here a tolerably strong ano- 

 malous dispersion; but whether this depends upon the ad- 

 mixture of platinum or belongs to the platinum oxide cannot 

 be determined. 



The oxides of iron, nickel, copper, and bismuth show normal 

 dispersion according to the above observations. 



Gold with Gold Oxide. 



I may remark that I had considerable trouble in preparing 

 prisms of pure metallic gold. Those obtained by disintegra- 

 tion of a, gold kathode almost all gave larger indices of 

 refraction than those put down in the table on p. 7 ; this 

 appears to result from the presence of traces of oxides of gold. 

 So also with the prisms electrolytic-ally deposited from solution 

 of gold potassium cyanide, some of them gave larger indices 

 of refraction. 



It is possible that with the intensity of current employed 

 small quantities of compounds of gold of different kinds might 

 be deposited with the metallic gold. 



The prisms which gave exceptional results were not green 

 by transmitted light like those used above for measurement, 

 but more or less violet, and occasionally even an intense 

 reddish-violet. I give the following examples: — 



No. 



c\ 



Red. White. Blue 



Red. White. Blue 



Electrolytically deposited. Greenish violet by transmitted light. 

 9-98 | +0-83 | ... | +2-47 || 104 j ... | 1«25 



Obtained by disintegration of a kathode in vacuo. 

 7-70 | -0-82 | -0-07 , +2v>5 | 0-89 | 0-99 | 1*38 

 Prepared by disintegration of a kathode in air at low pressure. 

 Bright red, with small metallic lustre. Contains only little 

 metallic gold. 

 3647 ... +37-77 ... || ... | 2-03 | 



