of Gold and other Metals to Light. 515 
pension only, is also shown by the deposit which occurs when 
they are left at rest. If the gold be comparatively abundant, a 
part will soon settle, 7. e. in twenty-four or forty-eight hours ; 
but if the preparation be left for six or eight months, a part will 
still remain suspended. Even in these portions, however, the 
diffused state of the gold is evident ; for where, as in some cases, 
the top to the depth of half an inch or more has become clear, 
it is seen that the ruby portion below is as a cloud sinking from it ; 
and in the part which has apparently been cleared from colour 
by the settling of the particles, the lens and cone of light still 
show the few, or rather the fine diffused particles yet in suspen- 
sion, though the protochloride of tin can show no gold in solu- 
tion. The mould or mucus before spoken of, often collects the 
larger, heavier particles, and becomes of a dark blue colour; it 
may then be taken out by a splinter of wood, and being shaken 
in water, disengages the particles, which issue from it in clouds 
like the sporules from a ripe puff-ball. 
A gradual change goes on amongst the particles diffused 
through these fluids, especially in the cases where the gold is com- 
paratively abundant. It appears to consist of an aggregation. 
Fluids, at first clear or almost clear to ordinary observation, 
become turbid ; being left to stand for a few days, a deposit falls. 
If the supernatant fluid be separated and left to stand, another 
deposit may be obtained. This process may be repeated, and 
whilst the deposition goes on, the particles in the fluid still seem 
to aggregate ; it is only when the fluid is deprived of much gold 
that the process appears to stop. Even after the fluid has 
attained a fine marked ruby tint, if allowed to stand for months 
in a place of equable temperature, the colouring particles will 
appear in floating clouds, and probably the aggregation is then 
still going on. That the particles of gold when they touch 
each other do in many cases adhere together with facility, is 
shown in many experiments. In order to test this matter me- 
chanically, I gave much agitation to a dense ruby fluid, but did 
not find it cause any sensible change in the character. When 
gold particles of a much larger size were agitated in water, they 
did cohere together, and the fluid, which required a certain time 
for settling at the beginning of the experiment, settled in a much 
shorter time at the termination. 
If these fluids be examined generally their appearances differ, 
not merely under different circumstances, but also under the same 
circumstances, though they always consist of a colourless hquid 
and diffused particles of gold. <A certain fluid in a bottle or 
glass, looked at from the front, 7. e. the illuminated side by 
general daylight, may appear hazy and amethystine, whilst in 
bright sunlight it will appear light brown and almost opake. 
212 
