522 Prof. Faraday on the Experimental Relations 
weak degree. So also does soda. Lime-water produces a change 
in the same direction, but the gold quickly precipitates associated 
with the lime. 
Ammonia causes the ruby fluid to assume a violet tint; the 
deposit is slow of formation and often ruby in colour; the alkali 
apparently retards the action of common salt. 
Chlorine or nitromuriatic acid turns the ruby fluid blue or 
violet-blue before they dissolve the gold. 
Solution of sulphuretted hydrogen changes the ruby slowly 
to purple, and finally to deep blue. AXther, alcohol, camphine, 
sulphide of carbon, gum, sugar, and glycerine cause little or no 
change in the fluids; but glycerine added to the dense deposits 
causes serious condensation and alteration of them, so that it 
could not be employed as a medium for the suspension of par- 
ticles in the microscope. 
All endeavours to convert the violet gold back into ruby were 
either failures, or very imperfect in their results. A violet fluid 
will, upon long standing, yield a deposit and a supernatant ruby 
fluid, but this I believe to be a partial separation of a mixture of 
violet and ruby gold, by the settlement of the blue or violet gold 
from ruby gold, which remains longer in suspension. Mucus, 
which often forms in portions of these fluids that have been exposed 
to the air, appears sometimes to render a fluid more ruby, but 
this it does by gathering up the larger violet particles; it often 
becomes dark blue or even black by the particles of gold adhering 
to it, many of which may be shaken out by agitation in water ; 
but I never saw it become ruby coloured as a filter can, and I 
think that in these cases it is the gathering out of the blue or 
violet particles which makes the fluid left appear more rubyin tint. 
I have treated blue or violet fluid with phosphorus in various ways, 
but saw no appearance of a return in any degree towards ruby. 
Sometimes the fluids possess a tendency to re-solution of the 
gold, a condition which may often be given by addition of a very 
little nitric acid, but im these cases the gold does not become 
ruby before solution. It would rather appear that the finer ruby 
particles dissolve first ; for the tint of the fluid, if ruby-violet 
at the commencement, changes towards blue. One effect only 
seemed to show the possibility of a reversion. Filtering-paper 
rendered ruby by a ruby fluid was washed and dried; being 
wetted by solution of caustic potash, it did not change; but 
being heated in a tube with the alkali, it became of a gray-blue 
tint ; pouring off the alkali, washing the paper, and then adding 
dilute sulphuric or nitric acid to it, there was no change; but on 
boiling the paper in the mixed acids there was a return, and when 
the paper was washed and dried, it approached considerably to 
the original ruby state. Again, potash added to it, rendered it 
