1857.] of Gold (and other Metals) to Light. 427 



particles 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 trans- 

 mitted 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 

 separated 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 re- 

 duces 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 pre- 

 sent 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. If the skin 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 light or not, the inner 

 membrane will become 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 parti- 

 cles 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-crystal, and then heated over a spirit-lamp 



