OF GOLD (AJS^D OTHEE METALS) TO LIGHT. 
153 
finer, the transmitted tint became ruby or violet-ruby, and this tint was especially see* 
when the deposit was caught on a card. As to the reflected light, even at these faintest 
parts it is golden and metallic. This is easily observed by wiping otf a sharp line across 
the deposit on glass in the very faintest part, and then causing the sun’s rays collected 
in the focus of a small lens to travel to and fro across that edge ; the presence of the 
metalhc gold on the unwiped part is at once evident by the high illumination produced 
there. It is evident that all the colours described are produced by one and the same 
substance, namely gold, the only apparent difference being the state of division and 
different degrees of the application of heat. The thickest parts of these deposits are so 
discontinuous, that they cannot conduct the electricity of a battery of two or three pairs 
of plates, i. e. of a battery unable to produce a spark among the particles. 
WTien any of these deposits of divided gold are heated to dull redness, a remarkable 
change occurs. The portions which before were violet, blue, or green by transmitted 
light, now change to a ruby, still preserving their metallic reflecting power, and this 
ruby is in character quite like that which is presented in the arts by glass tinged by gold. 
This change is often far better sho-wn in the more distant and thinner parts of the 
deposit, than in those nearest to the line of discharge, for near the latter place, where 
the deposit is most abundant, the metal appears to run up into globules, as with gold- 
leaf, and so disappears as a film. I beheve that the ruby character of the deposit in 
the line of discharge, is caused by the same action of heat produced at the moment 
by the electricity passing there. In the distant parts, the deposit, rubified by after heat, 
is not imbedded or fused into the glass, rock-crystal, topaz, &c., but is easily removed 
by a touch of the Anger, though in parts of the glass plate which are made very hot, it 
will adhere. 
If the agate pressure before spoken of, in respect of gold-leaf, be applied to ruby 
parts not too dense, places will easily be found where this pressure increases the reflect- 
ive power considerably, and where at the same time it converts the transmitted ray from 
ruby to green ; making the gold, as I believe, then accord in condition with beaten gold- 
leaf. On the other hand, if parts of the unhealed electric deposit, where they are purple- 
grey, and so thin as to be scarcely visible without care, be in like manner pressed, they 
will acquire the reflective power, and then transmit the green ray ; and I think I am 
justified by my experiments in stating, that fine gold particles, so loosely deposited that 
they -will wipe off by a light touch of the finger, and possessing one conjoint structure, 
can in one state transmit light of a hlue-grey colour, or can by heat be made to transmit 
light of a ruby colour, or can by pressure from either of the former states be made to 
transmit light of a green colour ; all these changes being due to modifications of the 
gold, as gold, and independent of the presence of the bodies upon which for the time 
the gold is supported; for I ought to have said, if I have not said so, that these changes 
happen with all the deposits upon glass, mica, rock-crystal, and topaz, and whatever the 
atmosphere in which they were formed. 
When gold is deflagrated by the voltaic battery near glass (I have employed sovereigns 
MDCCCLVII. T 
