172 
DE. FAEADAY ON THE EXPEEBIENTAL EELATIOXS 
sion of theii’ lustre and colour is gradual from the thickest to the thinnest, and the same 
is generally true, if thick films are gradually thinned and dissolved -whilst fioating on 
solvents ; the thick and the thin films must both be accepted as having the same amount 
of evidence for their metallic nature. When subjected to chemical agents, both the 
thick and the thin films have the same relations as pure metallic gold. These relations 
are not changed by the action of heat, yet heat shows the same pecuhar eflect that it had 
with preparations of gold obtained by beating, or by electric deflagrations. The remark- 
able and characteristic effect of pressure is here reproduced, and sometimes -with exti-a- 
ordinary results ; since from the favourable manner in which the particles are occasion- 
ally divided and then held in place on the glass, the mere touch of a finger or card is 
enough to produce the result. Yet with gold thus proved to be metallic, colours 
including grey, grey-violet, green, purple, ruby, especially by heat, and green again by 
pressiu'e, and by thinning of grey films, may be obtained by transmitted hght, almost all 
of them at pleasure. 
It may be thought that the fluid preparations present more difficulty to the admis- 
sion, that they are simply cases of pure gold in a divided state ; yet I have come to that 
conclusion, and believe that the differently-coloured fluids and particles are quite analo- 
gous to those that occur in the deflagrations and the films. In the first place they are 
produced as the films are, except that the particles are separated under the suiTace and 
out of the contact of the air ; still, when produced in sufficient quantity against the side 
of the containing vessel to form an adhering film, that film has every character of lustre, 
colour, &c. in the parts differing in thickness, that a film formed at the smTace has. 
Whilst the particles are diffused through the fluid it is difficult to deal with them by 
tests and reagents ; for their absolute quantity is very small and then’ physical characters 
are very changeable, chiefly as I believe by aggregation ; still there are some expedients 
which enable one to submit even the finest of them to proof. In several cases particles 
from ruby and amethystine fluids adhered to the sides of the bottles or flasks in which 
the fluids had been preserved, and the process of boihng seemed to favoiu’ such a result ; 
the adhesion was so strong, that when the fluid contents were removed and the bottles 
well washed, the glass remained tinged of a ruby or a violet colom-. These films, in 
which the fine particles were fixed mechanically apart and in place, were then submitted 
to the action of various chemical agents. Drying and access of air did not cause* any 
marked alterations in them. Strong nitric acid produced no change, nor hydi'ochloric 
acid, nor sulphuric acid. Neither did a solution of chloride of sodium, even up to brine, 
cause any alteration in the colour or any other character of the deposit. A httle solu- 
tion of chlorine or of nitromuriatic acid dissolved them at once, producmg the ordinary 
solutions of gold. I can see no other mode of accounting for these effects (wiiich are in 
strong contrast with what happens when ruby fluid is acted on by these agents), than to 
suppose that the gold particles, being in a high state of di-vision, were retained in that 
state for the time by their adhesion to the glass. Of course chemical change was fr’ee 
to occur, but not a change dependent upon their mutual aggregation ; yet they were not 
