OF GOLD (AOT) OTHEE METALS) TO LIGHT. 
163 
be in solid metallic particles, though of diJfferent sizes, it would seem that more light 
is transmitted and absorbed and less reflected by the finer particles than by the coarser 
set, the same quantity of gold being in the same space. I believe that there may be 
particles so fine as to reflect very little light indeed, that function being almost gone. 
Occasionally some of the fluids containing the very finest particles in suspension, when 
illuminated by the sun’s rays and a lens, appeared to give a fine green reflexion, but 
whether this is a true colour as compared to white light, or only the effect of contrast 
with the bright ruby in the other parts of the fluid, I am not prepared to say. 
WTien the deposits were examined in the dark tube by transmitted light, being first 
diffused in more or less water to give them the form of fluid, those first deposited, and 
therefore presumed to be the hea\ier and larger, transmitted a pure blue light. The second 
and the thu’d had the same character, perhaps the fourth, if the subdivision into portions 
had been numerous ; then came some which transmitted an amethystine ray from the 
white of paper ; and others followed progressing to the finest, which transmitted a rich 
ruby tint. It is probable that many of these deposits were mixtures of particles having 
different characters, and this is perhaps the reason that in some cases, when the fluids 
were contained in round-bottomed flasks, the lens-like 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 compa- 
ratively pm’e intermediate preparation transmitting a rub}'’ 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 hght 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 striae 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 likely to produce. However, 
upon regarding 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-Holet tint. Prevost showed in old times, how much the red and warm rays are 
reflected 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 
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