520 Prof. Faraday on the Experimental Relations 
sical 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 
division. They occur most readily where the particles are finest, 
i. e. in the ruby fluids, and so readily that it is difficult 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 will become blue or violet-blue, and sometimes almost co- 
lourless: 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. Ifthe 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, however, 
between this and the ruby may be obtained, and, as it appears 
to me, in either of two ways; for the intermediate fluid may be 
a mixture of ruby and violet 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 violet-blue state, I will, for brevity sake, describe that only 
in a particular manner. The violet or blue fluid, when examined 
by the sun’s rays and a lens, always gives evidence showing that 
the gold has not been redissolved, but is still in solid separate 
particles ; and this is confirmed by the non-action of protochlo- 
ride of tin, which, in properly prepared fluids, gives no indica- 
tion of dissolved gold. When a ruby solution is rendered blue 
by common salt, the separation of the gold as a precipitate is 
greatly hastened ; thus when 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 lower half of the fluid became blue whilst 
the upper remained ruby; in that state the cone of sun’s rays 
was beautifully developed in both parts. On standing for four 
hours the lower part became paler, a dark deposit of gold fell, 
and then the cone was feebly luminous there, though as bright as 
ever in the ruby above. In three days no cone was visible in the 
lower fluid ; a fine cone appeared in the upper. After many days 
the salt diffused gradually through the whole, first turningthe gold 
it came in contact with blue, and then causing its precipitation. 
Such results would seem to show that this blue gold is aggre- 
gated gold, 7. e. gold in larger particles than before, since they 
