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



from ruby to blue, such as could be effected on loose ruby 

 particles. Strong hydrochloric acid caused no change as long 

 as the tissue held together ; but as that became loose the gold 

 flowed out into the acid in ruby-amethystine streams, finally 

 changing to blue. Caustic potassa caused no change for days 

 whilst the tissue kept together, but on mixing all up by press- 

 ure the loosened gold became at last blue. Strong nitric acid 

 caused no change of colour until, by altering the tissue, the 

 gold particles first flowed out in ruby and amethystine streams, 

 and then were gradually changed to the condition of common 

 aggregated gold. All these effects, and the actions on light, 

 accord with the idea that the stain was simply due to diffused 

 particles of finely-divided gold ; and I am satisfied that all 

 such stains upon the skin, or other organic matter, are of ex- 

 actly the same nature. 



As to the gold in ruby glass, I think a little consideration is 

 sufficient to satisfy one that it is in the metallic condition. 

 The action of heat tends to separate gold from its state of 

 combination, and when so separated from the chloride, either 

 upon the surface of glass, rock-crystal, topaz, or other inactive 

 bodies, a ruby film of particles is frequently obtained. The 

 sunlight and lens show that in ruby glass the gold is in sepa- 

 rated and diffused particles. The parity of the gold glass, 

 with the ruby-gold deflagrations and fluids described, is very 

 great. These considerations, with the sufficiency of the as- 

 signed cause to produce the ruby tint, are strong reasons, in 

 the absence of any to the contrary, to induce the belief that 

 finely divided metallic gold is the source of the ruby colour. 



When a pure, clean, stiff jelly is prepared, and mixed, whilst 

 warm and fluid, with a little dilute chloride of gold, as if to 

 prepare a ruby fluid, it gelatinizes when cold, and if left for 

 two or three days may become a ruby jelly ; sometimes, how- 

 ever, the gold in the jelly changes but little or changes to blue, 

 or it may happen that it is reduced on the surface as a film, 

 brilliant and metallic by reflected light, and blue-grey by trans- 

 mitted light. I have not yet ascertained the circumstances 

 determining one or the other state. If a trace of phosphorus 

 in sulphide of carbon be added to the solution of gold in a 

 dilute state, arid some salt be added to the warm jelly, and the 

 latter be then mixed gradually and with agitation with the gold 



