of Gold and other Metals to Light. 411 
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 elec- 
tricity of a battery of two or three pairs of plates, 7. e. of a bat- 
tery unable to produce a spark among the particles. 
When 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 shown in the more distant and thinner parts of the de- 
posit, 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 disap- 
pears asa film. I believe that the ruby character of the deposit 
wm 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 im- 
bedded or fused into the glass, rock-crystal, topaz, &c., but is 
easily removed by a touch of the finger, 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 reflective power con- 
siderably, and where at the same time it converts the trans- 
mitted 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 unheated electric deposit, where they are 
purple-gray, 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 blwe-gray 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 
