OP GOLD (AND OTHEE METALS) TO LIGHT. 
165 
The particles in these fluids are remarkable for a set of physical alterations occasioned 
by bodies in small quantities, which do not act chemically on the gold, or change its 
intrinsic nature ; for through all of them it seems to remain gold in a fine state of divi- 
sion. They occur most readily where the particles are finest, ^. e. in the ruby fluids, and 
so readily that it is difiicult to avoid them ; they are often occasioned by the contact of 
vessels which are supposed to be perfectly clean. An idea of their nature may be 
obtained in the following manner. Place a layer of ruby fluid in a clean white plate, 
dip the tip of a glass rod in a solution of common salt and touch the ruby fluid ; in a few 
moments the fluid Avill become blue or violet-blue, and sometimes almost colourless : by 
mingling up the neighbouring parts of the fluid, it will be seen how large a portion of it 
can be affected by a small quantity of the salt. By leaving the whole quiet, it will be 
found that the changed gold tends to deposit far more readily than when in the ruby 
state. If the experiment be made with a body of fluid in a glass, twelve or twenty-four 
hours will suffice to separate gold which in the ruby state has remained suspended for 
six months. 
The fluid changed by common salt or otherwise, when most altered, is of a violet-blue, 
or deep blue. Any tint, howeAm*, betAA^een this and the ruby may be obtained, and, as it 
appears to me, in either of tAvo Avays ; for the intermediate fluid may be a mixture of 
ruby and Aiolet fluids, or, as is often the case, all the gold in the fluid may be in the state 
producing the intermediate colour ; but as the fluid may in all cases be carried on to the 
final Aiolet-blue state, I aauII, for breAity sake, describe that only in a particular manner. 
The Aiolet or blue fluid, when examined by the sun’s rays and a lens, always gives 
evidence shoAving that the gold has not been redissolved, but is still m solid separate 
particles ; and this is confirmed by the non-action of protochloride of tin, Avhich, in pro- 
perly prepared fluids, gwes no indication of dissolved gold. When a ruby solution is 
rendered blue by common salt, the separation of the gold as a precipitate is greatly 
hastened; thnsAvhen a glass jar containing about half a pint of the ruby fluid had a few 
drops of brine added and stirred into the lower part, the loAver half of the fluid became 
blue whilst the upper remained ruby ; in that state the cone of sun’s rays Avas beautifully 
deA'eloped in both parts. On standing for four hours the loAver part became paler, a 
dark deposit of gold fell, and then the cone Avas feebly luminous there, though as bright 
as ever in the ruby above. In three days no cone Avas visible in the lower fluid ; a fine 
cone appeared in the upper. After many days the salt diffused gradually through the 
whole, first turning the gold it came in contact Avith blue, and then causing its precipi- 
tation. 
Such results Avould seem to shoAv that this blue gold is aggregated gold, ^. e. gold in 
larger particles than before, since they precipitate through the fluid in a time which is as 
nothing to that required by the particles of the ruby fluid from which they are obtained. 
But that the blue particles are ahvays merely larger particles does not seem admissible 
for a moment, inasmuch as Aiolet or blue fluids may be obtained in which the particles will 
remain in suspension as long as in the ruby fluids ; there is probably some physical 
