312 Mr. Faraday on Divided Gold. [June 13, 



at the bottom, like a lens of deep coloured fluid, opaque at the mid- 

 dle, but deep ruby at the edges ; when agitated they may be again 

 diffused through the liquid. These particles tend to aggregate into 

 larger particles, and produce other effects of colour. It is found 

 that boiling gives a certain degree of permanence to the ruby state. 

 Many saline and other substances affect this ruby fluid : thus, a few 

 drops of solution of common salt being added, the whole gradually 

 becomes of a violet colour ; still the particles are only in suspension, 

 and when illuminated by a lens are a golden yellow by reflected 

 light : they separate now much more rapidly and perfectly by 

 deposition from the fluid than before. Some specimens, however, 

 of the fluid, of a weak purple or violet colour, remain for months 

 without any appearance of settling, so that the particles must be 

 exceedingly divided ; still the rays of the sun or even of a candle 

 in a dark room, when collected by a lens, will manifest their 

 presence. The highest powers of the microscope have not as yet 

 rendered visible either the ruby or the violet particles in any of 

 these fluids. 



Glass is occasionally coloured of a ruby tint by gold ; such 

 glass, when examined by a ray of light and a lens, gives the opalescent 

 effect described above, which indicates the existence of separate par- 

 ticles ; at least such has been the case with all the specimens Mr. 

 Faraday has examined. It becomes a question whether the con- 

 stitution of the glass and the ruby fluids described is not, as regards 

 colour, alike. At present, he believes . they are ; but whether the 

 gold is in the state of pure metal, or of a compound, he has yet to 

 decide. It would be a point of considerable optical importance if 

 they should prove to be metallic gold ; from the effects presented 

 when gold wires are deflagrated by the Leyden discharge over glass, 

 quartz, mica, and vellum, and the deposits subjected to heat, pres^ 

 sure, &c., he inclines to believe they are pure metal. 



[M. F.] 



