170 
DE. FAEADAT OX THE EXPEEBIEXTAL EELATIOXS 
cipitate fell and more quickly. Acid very much reduced this in quantity, dissolving out 
oxide of tia, and leaving httle else than tinely-di\ided gold, which, when diffused and 
examined in the dark tube, transmitted a blue colour. I heheve 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 particles first appeared, and then a blue deposit of 
larger particles, whilst the side and bottom of the glass became covered by an adheiing 
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 hght, and gave a good cone by the sun’s rays 
and lens. The blue colour was not deep, though all the gold had been separated from 
solution ; the preparation closely resembled that made uith protosulphate of iron and a 
little acid. 
A weak solution of gold, mingled with a httle sugar, being heated, fielded a ver}' 
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 httle glyce- 
rine with solution of gold reduces it at common temperatures, producmg 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, hght if present assisting the action ; and 
they afford valuable evidence in aid of the solution of the question relative to the con- 
dition of the metal m the divided state. If the sldn be touched with a solution 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 hght or not, the inner membrane uill become so stained, that 
though of a dull purple colour by common observation, a transmitted ray uill show it to 
be generally a very fine ruby, equal to that of ruby-coloured glass, or the gold fliuds 
already described, though perhaps in places of a beautiful tiolet hue. The character of 
the particles which are here located and not allowed to diffiise and aggregate, as in the 
fluids, will be resumed when deahng 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-crystal, and then heated over a 
spuit-lamp until the gold is reduced, it mil generally be found that the vapour has 
carried a portion of gold on to the neighbouring part of the glass, and that this part, 
when placed over a sheet of white paper, has the ruby tint. With the rock-ciystal both 
ruby and blue parts are produced; and when the ruby parts are subjected to rock- 
crystal pressure, they become beautifully green. In the arts also glass is oftentimes 
coloured ruby by gold ; I think that glass in this state derives its coloiu- tiom diffused 
divided gold ; and if either the ruby glass or the watch-glass be examined by a lens and 
