148 
DE. FAEADAT ON THE EXPEEBIENTAL EELATIONS 
sensible distortion of an object seen through it, that object being the line of light 
reflected from a tine wire in the focus of a moderate microscope. Xor perhaps was any 
distortion due to consecutive convexities and concawties to he expected ; for when the 
thicker parts of the leaf were examined they seemed to he accumulated plications of the 
gold, the leaf appearing as a most irregular and crumpled object, with dark veins run- 
ning across both the thicker and thinner parts, and from one to the other. Yet in the 
best microscope, and with the highest power, the leaf seemed to he continuous, the 
occurrence of the smallest sensible hole making that continuity at other parts apparent, 
and every part possessing its proper green colom*. How such a film can act as a plate on 
polarized light in the manner it does, is one of the queries suggested by the phenomena 
which requires solution. 
When gold-leaf is laid upon glass and its temperatm-e raised considerably without 
disturbance, either by the blowpipe or an ordinary Ai’gand gas-brnmer, it seems to dis- 
appear, e. the lustre passes away, the light transmitted is abundant and nearly white, 
and the place appears of a pale brown colour. One would think that much of the metal 
was dissipated, but all is there, and if the heat has been very high (which is not neces- 
sary for the best results), the microscope shows it in minute globular portions. A com- 
paratively low heat, however, and one unable to cause separation of the paidicles, is known 
to alter the molecular condition of gold, and the gold-beater finds important advantage 
in the annealing effect of a temperature that does not hurt the skins or leaves between 
which he beats the metal. 
It might be supposed that the annealed metal, in contracting from the constrained 
and attenuated state produced by beating, drew up, leaving spaces tlirough which white 
light could pass, and becoming itself almost insensible through the smallness of its 
quantity ; and if gold-leaf unattached to glass be heated carefully Avith oil in a tube, it 
does shrink up considerably even before it loses its green colour, Avhich finally happens. 
But if the gold-leaf laid upon glass plates by Avater only be carefully dried, then intro- 
duced into a bath of oil and raised to a temperature as high as the oil can bear for five 
or six hours, and then suffered to cool, the plates, AAdien taken out and Avashed, fii’st in 
camphine and then in alcohol, present specimens of gold which has lost its green colom-, 
transmits far more light than before and reflects less, AA'hilst yet the film remains in form 
and other conditions apparently quite unchanged. Bemg noAV exammed m the micro- 
scope, it presents exactly the forms and appearance of the origmal leaf, except m coloiu ; 
the same irregularities appear, the same continuity, and if the destruction of the green 
colour has not been complete, it Avill be seen that it is the thicker folds and parts of the 
mottled mass that retaias the original state longest. 
This change does not depend upon the substance in contact AAith AA'hich the gold is 
heated *. If the leaf be laid upon mica, rock-crystal, silver or platinum, the same result 
* The disappearance of gold-leaf as metal, when mingled with lime, alumina and other bodies, and then 
heated, has been already observed ; and referred to oxidation (J. A. Buchxeu). See Gmelin’s ‘Chemistry,’ 
vi. p. 206, “ Purple oxide of gold.” 
