171 
OF OOLD (Al^D OTHEE METALS) TO LIGHT. 
the cone of rays, it will be seen that the colours are not due to any gold dissolved, but 
to solid and diffused particles. There is nothing in any of the appearances or characters, 
or in the processes resorted to to obtain the several effects, that point at any physical 
difference in the nature of the results ; and -without saying that gold cannot produce a 
ruby colour whilst in combination or solution, I think that in all these cases the ruby 
tint is due simply to the presence of diffused finely-di-vided gold. 
Metallic character of the divided gold. 
Hitherto it may seem that I have assumed the various preparations of gold, whether 
ruby, green, violet, or blue in colour, to consist of that substance in a metallic dmded 
state. I -vHll now put together the reasons which cause me to draw that conclusion. 
With regard to gold-leaf no question respecting its metallic nature can arise, but it 
offers e-vidence reaching to the other preparations. The green colour conferred by 
pressure, and the removal of this colour by heat, evidently belong to it as a metal ; these 
effects are very striking and important as regards the action on light, and where they 
recur with other forms of gold, may be accepted as proof that the gold is in the metallic 
state. Although I do not attach equal importance to the fact akeady described, that 
gold-leaf frequently presents fine parts that appear to be ruby in colour, I am not as 
yet satisfied that they are not in themselves ruby ; and if they should be so, it will be 
another proof by analogy of the metalhc natm’e of other kinds of preparations eminently 
ruby. 
The deflagrations of gold wire by the Leyden discharge can be nothing but divided 
gold. They are the same whatever the atmosphere surrounding them at the time, or 
whatever the substance on which they are deposited. They have all the chemical reac- 
tions of gold, being, though so finely di-vided, insoluble in the fluids that refuse to act 
on the massive metal, and soluble in those that dissolve it, producing the same result. 
Heat makes these divided particles assume a ruby tint, yet such heat is not likely to 
take away them metallic character, and when heated they still act with chemical agents 
as gold. Pressure then confers the green colour, which heat takes away, and pressure 
reconfers. All these changes occur with particles attached to the substances which 
support them by the slightest possible mechanical force, just enough indeed to prevent 
their coalescence and to keep them apart and in place, and yet offering no resistance to any 
chemical action of test agents, as the acids, &c., not allo-wing any supposition of chemical 
action between them and the body supporting them. Still this gold, unexceptionable 
as to metalhc state, presents different colours when -viewed by transmitted fight. Ruby, 
green, violet, blue, &c. occur, and the mere degree of division appears to be the deter- 
mining cause of many of these colours. The deflagrations by the voltaic battery lead to 
the same conclusion. 
The gold films produced by phosphorus have every character belonging to the metallic 
state. TV hen thick, they are in colour, lustre, weight, &c. equal to gold-leaf, but in the 
unpressed state, their transmitted colour is generally grey, or violet-grey. The progres- 
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