174 
DE. FAEADAY OX THE EXPEEDIEXTAL EELATIOXS 
reverse change. Particles transmitting blue light could be obtained in such quantity as 
to admit of their being washed and dried in a tube, and being so prepared they pre- 
sented every character of gold: when heated, no oxygen, water, phosphorus, acid of 
])hosphorus, nor any other substance was evolved from them : they changed a little, as 
the film when heated changed, becoming more reflective and of a pale brown colour, 
and contracted into aggregated porous masses of pure ordinary gold. 
Gold is reduced from its solution by organic tissues ; and stained gut has been quoted 
as a case. I have a very fine specimen which by transmitted hght is as pure a ruby as 
gold-stained glass, and I believe that the gold has been simply reduced and drflPused 
through the tissue. The preparation stood all the trials that had been applied to the 
ruby 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 par- 
ticles. 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 pressure the loosened gold became at last blue. 
Strong nitric acid caused no change of colour until, by altering the tissue, the gold par- 
ticles 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 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 surfac-e 
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 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, 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-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, and some salt be added to the warm jelly, and the latter be then mixed 
gradually and with agitation with the gold solution, a ruby jelly is generally produced. 
