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



It would rather appear that the finer ruby particles dissolve 

 first, for the tint of the fluid, if ruby- violet 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 grey-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 considerably to the original 

 ruby state. Again, potash added to it rendered it blue, which 

 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 which may be considered 

 the surface of the particles. 



The state of division 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 division, 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 ; for judging 

 of their magnitude by the time occupied in their descent through 

 the fluid, it would appear that violet 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 undepo- 

 sited 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, varying their depth, until 

 the light from white paper, transmitted through them, was 

 apparently equal to that transmitted by the standard glass. 

 Then known quantities of these ruby fluids were evaporated 

 to dryness, the gold converted into chloride, and compared by 

 reduction on glass and otherwise with solutions of gold of 

 known strengths. A portion of chloride of gold, containing 



