518 Prof. Faraday on the Experimental Relations 
deposit was ruby at the edges, though deep violet in the middle, 
the former having settled last ; but as a pure blue deposit could 
be obtained, and also one transmitting a pure ruby ray, and as 
a comparatively pure intermediate preparation transmitting a 
ruby violet, or amethystine ray, was obtained, it is probable that 
all gradations from blue to ruby exist; for the production of 
which I can see no reason to imagine any other variation than the 
existence of particles of intermediate sizes or proportions. 
When light other than white was passed through the fluids, 
then of course other tints were produced, yet some of these were 
unexpected. A fluid of a pure blue colour, whilst in the dark 
tube, would in an open glass and by reflected light appear of a 
strong ruby-violet tint. Dropping some of the wet deposit into 
pure water, the striz which it formed would in one part be ruby 
in colour and in another violet: these effects were referable to 
the light reflected from the solid particles back through the 
fluid to the eye, but it seemed redder than any which light 
reflected from gold was hkely to produce. However, upon re- 
garding the surface of dull gold-leaf, or the thick wet deposit of 
gold, or the hand, it was found that the red rays easily passed 
through the blue fluid and formed a ruby-violet tint. Prevost 
showed in old times, how much the red and warm rays are re- 
flected by gold,in preference to the others contained in white light. 
The supernatant fluid in specimens that had stood long and 
deposited, was always ruby; yet because it showed no dissolved 
gold, because it showed the illuminated cone by the lens, and 
because by standing ruby clouds settled in it, there was every 
reason to believe that the gold was there in separated particles, 
and that such specimens afforded cases of extreme division, which 
by long standing would form deposits of the finest kind. 
Those fluids which on standing gave abundance of deposits, 
transmitting blue light, consisted in the first instance of particles 
transmitting a ruby light, and in these cases it would seem that 
the particles at their first separation were always competent to 
transmit this ruby light; and if the preparation were not too 
rich in gold the ruby condition appeared to be retained, the 
division being then most extreme. But purple or amethystine 
fluids could be procured, which, containing no colouring parti- 
cles other than suspended gold, still retained them in suspension 
for many months together, so that they must have been as light 
or as finely divided as those in the ruby fluids. When the phos- 
phorous ether was employed for the reduction of the gold, such 
fluids occurred; also when the solution of the phosphorus in 
sulphide of carbon was used, provided the solution of gold had 
a very little chloride of sodium contained in it. They appear to 
show that the mere degree of division is not the only circumstance 
