151 
OF GOLD (A]^D OTHEE METALS) TO LIGHT. 
appeared too unsubstantial and translucent for that ; but when pressed together it clung 
and adhered hke clean silver, and resumed all its metallic characters. 
^\Tien the silver is much heated, there is no doubt that the leaf runs up into particles 
more or less separate. But the question 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 natime 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 fur- 
nish any process which can instruct us as to this condition, for all the operations of 
polishing, burnishing, &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 retm-n 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 transmitted light, present the 
appearance of red parts ; these parts are small, and often in curved lines, as if a fine hair 
had been there during the beating. At first I thought the gold was absolutely red in 
these parts, but am mclined to believe that in the greatest number of cases the tint is 
subjective, being the result of the contrast between the white light transmitted through 
bruised parts, and the green light of the neighbouring continuous parts. Nevertheless, 
some of these places, when seen in the microscope, appeared to have a red colour of their 
own, that is, to transmit a true red light. As I believe that gold in a certain state of 
di\ision can transmit a ruby light, I am not prepared to say that gold-leaf may not, in 
some cases, where the effect of pressure in a particular direction has been removed, do 
the same. 
Many of the prepared films of gold were so thin as to have their reflective power con- 
siderably reduced, and that in parts which, under the microscope and in other ways, 
appeared to be quite continuous : this agrees with the transmission of all the rays affeady 
mentioned, but it seems to imply that a certain thickness is necessary for full reflexion ; 
therefore, that more than one particle hi depth is concerned in the act, and that the 
division of gold into separate particles by processes to be described, may bring them 
within or under the degree necessary for ordinary reflexion. 
As particles of pure gold wall be found hereafter to adhere by contact, so the process 
of beating may be considered as one >vhich tends to weld gold together in all directions, 
and especially in that transverse to the blow, — a point favourable to continuity in that 
dmection, both as it tends to preserve and even reproduce it. 
