164 
DE. FAEADAT THE EXPEEBIEXTAL EELATIO^'S 
it would seem that the particles at their first separation were always competent to trans- 
mit this ruby light ; and if the preparation were not too rich in gold the ruby condition 
appeared to be retained, the division being then most extreme. But purple or ame- 
thystine fiuids could be procured, which, containing no colouring particles other than 
suspended gold, still retained them in suspension for many months together, so that they 
must have been as light or as finely divided as those in the ruby fiuids. 'SMien the 
phosphorous ether was employed for the reduction of the gold such fiuids occurred ; also 
when the solution of the phosphorus in sulphide of carbon was used, provided the solu- 
tion of gold had a very little chloride of sodium contained in it. They appear to show 
that the mere degree of division is not the only circumstance which deteimines the 
aptitude to transmit in preference this or that ray of light. 
Considering the fluids as owing their properties to difiirsed particles, it may be obsen'ed. 
that many of them which in small quantities in the dark tube transmit an amethystine 
light, send forward a ruby light when the quantity is increased ; and this appears to be 
the general progression. I have not found any which by increase in quantity tended to 
transmit the blue rays in preference to the red. 
Elevation of temperature had an effect upon these fluids which is advantageous in 
their preparation. On boiling an apparently clear ruby fluid for some time, its colour- 
passed a little towards amethystine, and on boiling a like amethystme fluid, its tmt 
passed towards blue. The separation of the gold particles was also facihtated, for now 
they would settle in three or four days from a fluid which, prior to this operation, would 
not have deposited them in an equal degree for weeks. In the case of the ruby fluids 
the colour often became more rosy and luminous, and by reflected hght the fluid seemed 
to have became more turbid, as if the particles had gained in reflective power ; in fact 
the boiling often appeared to confer a sort of permanency on the particles in their new- 
state. When settled, they formed collections looking like little lenses of a deep ruby or 
violet colour, at the bottom of the flasks containing the fluid ; when all was shaken up 
the original fluid was reproduced, and then, by rest, the gold re-settled. This effect could 
be obtained repeatedly. The particles could fall together wflthin a certain hmit, but 
many weeks did not bring them nearer or into contact ; for they remained free to be 
diffused by agitation. The space they occupied in this lens-like form must have been a 
hundredfold, or even a thousandfold, more than that, wdiich they would have filled as 
solid gold. Whether the particles be considered as mutually repulsive, or else as mole- 
cules of gold with associated envelopes of water, they evidently differ in their physical 
condition, for the time, from those particles which by the application of salt or other 
substances are rendered mutually adhesive, and so fall and clot together. 
In preparing some of these fluids, I made the solution of gold hot and boiling before add- 
ing the solution of phosphorus. The phenomena were the same in kind as before: but when 
the phosphorus was dissolved in sulphide of carbon, the gold soon fell as a dark flocculent 
deposit ; when it was dissolved in ether a more permanent turbid ruby fluid was obtained, 
which, if it does not go on changing in aggregation, may give a good ruby deposit. 
