408 Prof. Faraday on the Experimental Relations 
the muffle or by a blowpipe, which is necessary to fuse the metal 
and make it run together in globules, is very much higher than 
that which causes the first change of the silver: the latter is, in 
fact, below such a red heat as is just visible in the dark. What- 
ever the degree of heat applied, the metal remains as metallic 
silver during the whole time. When many silver leaves were laid 
loosely one upon another, rolled up into a loose coil, introduced 
into a glass tube, and the whole placed in a muffle and heated 
carefully for three or four hours to so low a degree that the glass 
tube had not been softened or deformed, it was found that the 
silver-leaf had sunk together a little and shaped itself in some 
degree upon the glass, touching by points here and there, but 
not adhering to it. But it was changed, so that the light of a 
candle could be seen through forty thicknesses: it had not run 
together, though it adhered where one part touched another. 
It did not look like metal, unless one thought of it as divided 
dead metal, and it even appeared too unsubstantial and translu- 
. cent for that; but when pressed together, it clung and adhered 
like clean silver, and resumed all its metallic characters. 
When the silver is much heated, there is no doubt that the 
leaf runs up. into particles more or less separate. But the ques- 
tion still remains as to the first effect of heat, whether it merely 
causes a retraction of the particles, or really changes the optical 
and physical nature of the metal from the beaten or pressed 
state to another from which pressure can return it back again to 
its more splendid condition. It seems just possible that the 
leaf may consist of an infinity of parts resulting from replications, 
foldings and scales, all laid parallel by the beating which has 
produced them, and that the first action of heat is to cause these 
to open out from each other ; but that supposition leaves many 
of the facts either imperfectly explained or untouched. The 
Arts do not seem to furnish any process which can instruct us 
as to this condition, for all the operations of polishing, burnish- 
ing, &c. applied to gold, silver and other metals, are just as 
much fitted to produce the required state under one view as 
under the other. 
To return to gold: it is clear that that metal, reduced to small 
dimensions by mere mechanical means, can appear of two 
colours by transmitted light, whatever the cause of the difference 
may be. The occurrence of these two states may prepare one’s 
mind for the other differences with respect to colour, and the 
action of the metallic particles on light, which have yet to be 
described. 
Many leaves of gold, when examined by a lens and trans- 
mitted light, present the appearance of red parts; these parts 
are small, and often in curved lines, as if a fine hair had been 
