of Gold and other Metals to Light. 581 
Gold is reduced from its solution by organic tissués; and 
stained gut has been quoted as a case. I havea very fine speci- , 
men which by transmitted light is as pure a ruby as gold-stained 
glass, and I believe that the gold has been simply reduced and 
diffused through the tissue. The preparation stood all the trials 
that had been applied to the raby films on glass or the gold 
deposit on filtering-paper. Portions of it remained soaking in 
water, solution of chloride of sodium and dilute sulphuric acid 
for weeks, but these caused no change from ruby to blue, such 
as could be effected on loose ruby particles. Strong hydro- 
chloric 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 to-. 
gether, but on mixing all up by pressure, the loosened gold 
hecame at last blue. Strong nitrie 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 exactly the same nature. 
As to the gold in ruby glass, I think a little consideration is 
sufficient to satisfy one that itis in the metallic condition. The 
action of heat tends to separate gold from its state of eombi- 
nation, 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 separated 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 assigned cause to pro- 
duce 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, however, 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-gray by transmitted light, 
I have not yet ascertained the cireumstances determining one or 
the other state. If a trace of phosphorus in sulphide of carbon 
he added to the solution of gold in a dilute state, and some salt 
2M2 
