440 On the Experimental Relations [1857. 



When the coloured jellies are laid upon glass plates and 

 allowed to dry, the plates introduced obliquely into the sul- 

 phide of carbon affect the ray, but not as gold films ; the light 

 image becomes visible, but the plane of polarization is not 

 changed ; the light is coloured by the ruby or blue tint of 

 the gold present, but a film of jelly without gold makes it 

 visible to the same extent. In this case the gold is not in one 

 plane, but diffused through the dry jelly, and the effect is the 

 same as if it were diffused through water, being negative. 



Such are the effects with the various preparations of divided 

 gold. I will hastily notice what occurs with some other metals. 

 Platinum deflagrated in hydrogen : it depolarized the ray, 

 required direct rotation of the analyser to attain a minimum, 

 therefore rotated the plane of polarization ; but did not pre- 

 sent sensible colour on either side of the minimum of light. 

 Palladium deflagrated in hydrogen : it depolarized, producing 

 a red image ; direct rotation of the analyser lessened the light 

 to a minimum, and then brought in a blue image. The films 

 of palladium obtained by phosphorus acted well in the same 

 manner. These films appear to be exceedingly continuous, 

 and it could be observed in them, that though the thickest 

 were not the best, yet films could be obtained so thin as to be 

 distinctly inferior to other parts a little thicker ; also that where 

 the brilliancy of reflexion which indicates perfect smoothness 

 passed in any degree into dulness, the action of the film was 

 injured : the perfect condition of the surfaces of the films 

 seems to be essential to their good action. Rhodium films by 

 phosphorus gave good actions, like those produced by gold. 

 Silver deflagrations, either in air or hydrogen, gave depo- 

 larizing results like those with gold. Silver films also gave 

 excellent results of the like kind. A thin pale brown film was 

 much better than a thicker one. Copper deflagrated in hy- 

 drogen : depolarized, bringing in a red image, which by di- 

 rect rotation of the analyser was lowered a little, and then con- 

 verted to blue. The copper films obtained from oil acted in 

 the same manner ; the red and blue images appeared in their 

 order ; but very little direct rotation of the analyser was re- 

 quired to produce the minimum of light. Tin deflagrated in 

 hydrogen : depolarized and rotated the ray, as with gold ; the 

 images were only feeble in colour. Lead deflagrated in hy- 



