1857.] of Gold (and other Metals] to Light. 409 



must have been touching though they did not form a con- 

 tinuous film ; and on the other hand, the difference between 

 the effect here and with unattached gold-leaf, shows that the 

 degree of continuity as a film must be very small. When these 

 heated films were greened by agate pressure, or the drawing 

 pressure of a card, the green parts remained granulated, 

 apparently in the same degree as when purple. The green 

 was not subjective or an effect of interference, but a positive 

 colour belonging to the gold in that condition. Every touch of 

 the agate was beautifully distinct as a written mark. The parts 

 thus greened and the purple parts appeared to transmit about 

 the same amount of light. Though the film appeared gra- 

 nulated, no impression was made upon the mind that the 

 individual particles of which the film consisted were in any 

 degree rendered sensible to the eye. 



The unheated gold films when pressed by agate often 

 indicated an improved reflective power, and the light trans- 

 mitted was also modified ; generally it was less, and occasionally 

 tended towards a green tint ; but the effect of pressure was 

 by no means so evident as in particles which had been heated. 

 Films of some other metals were reduced by phosphorus in 

 like manner, the results in all these cases being of course 

 much affected by the strength of the solution and the time of 

 action ; they are briefly as follows : Palladium : a weak solu- 

 tion of the chloride gave fine films, apparently very continuous 

 and stiff;, the reflexion was strong and metallic, of a dark grey 

 colour ; the transmission presented every shade of Indian ink. 

 Platinum chloride gave traces of a film excessively thin, and 

 very slow in formation. Rliodium chloride in three or four 

 hours gave a beautiful film of metal in concentric rings, varying 

 in reflecting and transmitting power over light and also in 

 colour; those which reflected well, transmitted little light; 

 and those which transmitted, reflected little light; one migh 

 have thought there was no metal in some of the rings betwee 

 other rings that reflected brilliantly, but the metal was ther 

 of transmitting thickness ; the transmitted colour of rhodium 

 varied from brown to blue. Silver : a solution of the nitrate 

 gave films showing the concentric rings ; the light transmitted 

 by the thinner parts was of a warm brown, or sepia tint ; the 

 film becomes very loose and mossy in the thicker parts and is 



