1857.] of Gold (and other Metals) to Light. 419 



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 light the fluid seemed to have become 

 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 within a certain 

 limit, 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 hundred- 

 fold or even a thousandfold, more than that, which they would 

 have filled as solid gold. Whether the particles be considered 

 as mutually repulsive, or else as molecules of gold with asso- 

 ciated 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 adding 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 

 notgoon changing in aggregation, may give a good ruby deposit. 

 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 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 



