167 
OF GOLD (A^D OTHEE IVIETALS) TO LIGHT. 
All endeavours to convert the violet gold back into ruby vrere 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 \iolet 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 ruby in 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. Some- 
times 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 in these cases the gold does not 
become ruby before solution. It would rather appear that the finer ruby particles dis- 
solve first, for the tint of the fluid, if ruby-’siolet 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 con- 
siderably to the original ruby state. Again, potash added to it rendered it blue, whicli 
by washing with water, and especially with a little nitric acid, was much restored 
towards ruby. These changes may be due to an affection of the surface, or that whidi 
may be considered the surface of the particles. 
The state of dirision of these particles must be extreme ; they have not as yet been 
seen by any power of the microscope. Whether those that are ruby have their colour 
dependent upon a particular degree of dirision, or generally upon their being under a 
certain size, or whether it is consequent in part upon some other condition of the 
particles, is doubtful; forjudging of them magnitude by the time occupied in their descent 
through the fluid, it would appear that riolet and blue fluids occur giving violet deposits, 
which still consist of particles so small as to require a time equally long with the ruby 
particles for their deposition, and indeed in some specimens to remain undeposited in 
any time which has yet occurred since their formation. These deposits, when they occur, 
look like clear solutions in the fluid, even under the highest power of the microscope. 
I endeavoured to obtain an idea of the quantity of gold in a given ruby fluid, and for 
this purpose selected a plate of gold ruby glass, of good full colour, to serve as a standard, 
and compared different fluids with it, vaiyhig their depth, until the hght from white 
paper, transmitted through them, was apparently equal to that transmitted by the 
standard glass. Then knomr quantities of these ruby fluids were evaporated to drjmess. 
