524: Prof. Faraday on the Experimental Relations 
and the quantity of gold present, may not be always in the 
same proportion. I need hardly say that mere dilution does 
not alter the tint sensibly, 7. e. if a deep ruby fluid be put into a 
cylindrical vessel, and the eye look through it along the axis of 
the vessel, dilution of the fluid to eight or ten times its volume 
does not sensibly alter the hight transmitted. From these con- 
siderations, it would appear that one volume of gold is present 
in the ruby fluid in about 750,600 volumes of water; and that 
whatever the state of division to which the gold may be reduced, 
still the proportion of the solid particles to the amount of space 
through which they are dispersed must be of that extreme pro- 
portion. This accords perfectly with their invisibility in the mi- 
croscope ; with the manner of their separation from the dissolved 
state ; with the length of time during which they can remain 
diffused ; and with their appearance when illuminated by the 
cone of sun’s rays. 
The deposits, when not fixed upon glass or paper, are much 
changed by drying; they cannot be again wetted to the same 
degree as before, or be again diffused ; and the light reflected 
or refracted is as to colour much altered, as might be expected. 
Whilst diffused through water, they seem to be physical associ- 
ations of metallic centres with enveloping films of water, and as 
they sink together will lie for months at the bottom of the fluid 
without uniting or coming nearer to each other, or without beimg 
taken up by metallic mercury put into the same vessel. This 
is consistent with what we know of the manner in which gold 
and platinum can be thoroughly wetted if cleaned in water, and 
of the difference which occurs when they are dried and become 
invested with air. I endeavoured to transfer the gold particles 
unchanged into other media, for the purpose of noting any 
alteration in the action on light. By decanting the water very 
closely, and then carefully adding alcohol with agitation, I could 
diffuse them through that fluid; they still possessed a blue 
colour when looked through in the dark tube, but seemed much 
condensed or aggregated, for the fluid was obscure, not clear, 
and the particles soon subsided. I could not transfer them 
from aleohol to camphine; they refused association with the 
latter fluid, retaining a film of alcohol or water, and adhering 
by it to the glass of the vessel; but when the camphine was 
removed, a partial diffusion of them in fresh alcohol could be 
effected, and gave the colour as before. All these transfers, how- 
ever, injured the particles as to their condition of division. In 
one case I obtained a ruby film on a white plate ; on pouring off 
the water and allowing parts to become dry, these became violet, 
seen by the light gomg through them to the plate and back 
again to the eye. I could not wet these places with water, a 
