526 Prof. Faraday on the Experimental Relations 
larger quantity, a more bulky precipitate fell and more quickly. 
Acid very much reduced this in quantity, dissolving out oxide of 
tin, and leaving little else than finely-divided gold, which, when 
diffused and examined in the dark tube, transmitted a blue colour. 
I believe the purple of Cassius to be essentially finely-divided 
gold, associated with more or less of oxide of tin. 
Tartaric acid being added to a weak solution of gold gradually 
reduced it. The amethystine tint produced by diffused parti- 
cles first appeared, and then a blue deposit of larger particles, 
whilst the side and bottom of the glass became covered by an 
adhering film of finer particles, presenting the perfect ruby tint 
of gold. 
{Ether added to a weak solution of gold gradually reduced it ; 
the fluid was brown by reflected light, fine blue by transmitted 
light, and gave a good cone by the sun’s rays and lens. The 
blue colour was not deep, though all the gold had been sepa- 
rated from solution; the preparation closely resembled that 
made with protosulphate of iron and a little acid. 
A weak solution of gold, mingled with a little sugar, being 
heated, yielded a very characteristic decomposition. The gold 
was reduced into diffused particles, which rendered the fluid of a 
ruby-amethystine colour, and which, upon standing for twenty- 
four hours, gave signs of separation by settling as on former 
occasions. A little glycerine with solution of gold reduces it 
at common temperatures, producing a fluid, brown by reflexion, 
blue by transmission, giving a fine cone of rays by its suspended 
particles. Heat quickens the action, and causes a blue deposit. 
Organic tissues often reduce solutions of gold, light if present 
assisting the action; and they afford valuable evidence in aid of 
the solution of the question relative to the condition of the 
metal in the divided state. Ifthe skin be touched with a solu- 
tion of gold, it soon becomes stained of a dull purple colour. If 
a piece of the large gut of an ox be soaked first in water, then 
in a solution of gold, and be afterwards taken out and allowed to 
dry, either exposed to light or not, the inner membrane will be- 
come so stained, that though of a dull purple colour by common 
observation, a transmitted ray will show it to be generally a very 
fine ruby, equal to that of ruby-coloured glass, or the gold fluids 
already described, though perhaps in places of a beautiful violet 
hue. The character of the particles which are here located and 
not allowed to diffuse and aggregate, as in the fluids, will be 
resumed when dealing with the whole question of the metallic 
nature of the particles of the variously-divided gold. 
Chloride of gold is reducible by heat alone. If a drop of 
solution of chloride of gold be evaporated in a watch-glass, or 
on a plate of rock-erystal, and then heated over a spirit-lamp 
