1857.] of Gold (and other Metals] to Light. 441 



drogen : acted as tin. Iron deflagrated in hydrogen : acted 

 as tin. Zinc deflagrated in hydrogen : acted as tin. Aluminium 

 deflagrated in hydrogen : had like action with the rest ; the 

 image brought in by it was red, which direct revolution of the 

 analyser reduced at a little distance to a minimum, and then 

 converted to blue. A film of mercury produced by sublima- 

 tion, a film of arsenic produced in like manner, and a film of 

 smoke from a candle, though all of them sufficiently pervious 

 to light, did not produce any result of depolarization. Films 

 of the smoke of burning sine, of antimony, or of oxide of iron 

 produced no effect. 



I placed some metallic solutions in a weak atmosphere of 

 sulphuretted hydrogen. Gold and platinum gave no films ; 

 silver so poor a film as to be of no use ; and lead one so brittle 

 as to be unserviceable. That obtained with palladium I be- 

 lieve to be the metal itself. The films of sulphuret of mercury, 

 sulphuret of antimony which was orange, and sulphuret of 

 copper which was pale brown, all acted on the light, and de- 

 polarized it. The sulphuret of copper presented a difference 

 from the metals generally, worth recording ; it depolarized the 

 light, producing an image, which, if not blue at once, was 

 rendered blue by a little direct rotation of the analyser ; after 

 which the same motion brought in a minimum and then pro- 

 duced an orange or red tint, i. e. with the sulphuret of copper 

 the warm and cold tints appear on opposite sides of the 

 minimum to those where they occur when films of the metals 

 are employed, though the minimum in both cases is in the 

 same direction. 



Many of the results obtained in the sulphide of carbon were 

 produced also in camphine, the analyser being in each case 

 adjusted to the minimum of light before the metallic plate or 

 film was introduced. I pass, however, to a very brief account 

 of some polarizations effected by the metals themselves in the 

 sulphide of carbon, in which case the polarizing Nicol prism 

 was dispensed with. The results show that all the dry forms 

 of gold accord in giving the same manifestation of action on 

 light, whatever the state of their division, provided they be 

 disposed in a thin regular layer, equivalent to a continuous 

 film. It was first ascertained that a plate of crown-glass in an 

 inclined position in sulphide of carbon gave no signs of polarity 



