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Gold fluids. Whilst the particles of phosphorus are producing a 

 film on the surface, it frequently happens that streams of a red colour 

 descend from them through the fluid ; and if the phosphorus be sub- 

 merged, and left for twenty -four or forty-eight hours, this red product 

 is easily and abundantly obtained. If the gold solution be placed 

 in a very clean bottle, and then a few drops of a solution of phos- 

 phorus in ether be added, and the whole agitated from time to time, 

 the ruby fluid is obtained in a shorter period. This fluid is apt to 

 change in colour, becoming amethystine, violet, purple, and finally 

 blue ; impurities of certain kinds in very small quantities cause this 

 change. It is hardly possible to clean a vessel so well that the first por- 

 tion put into it does not alter. Most saline bodies produce the change ; 

 a trace of common salt readily makes it manifest. That all these 

 fluids are coloured by diffused particles is shown by the circumstance, 

 that on being left for a shorter or longer time, the particles sink, 

 forming a coloured stratum of deposit ; many months, however, are 

 required for even the partial separation of the finer ruby particles. 

 "When a light is looked at through the fluid, the latter appears trans- 

 parent ; but when the eye is on the illuminated side, then the fluid 

 is seen opalescent. If a cone of sun-rays be thrown by a lens into 

 the fluid, the illumination of the particles within the cone shows their 

 presence as undissolved bodies. It is believed that all the particles 

 being metallic gold, the ruby are in the finest state of division, the 

 blue in a more aggregated condition. Though the ruby particles, 

 whilst freely diffused, are easily changed in colour, and as it is sup- 

 posed by aggregation, still they may in some degree be separated by 

 a filter ; for on passing the fluid several times through a paper filter, 

 the latter associates much of the rubifying substance with itself, and 

 becomes of a rose colour ; it may then be well washed and dried, and 

 contains the ruby particles located, as it is believed, and prevented 

 by their attachment to the paper-fibres from undergoing mutual 

 aggregation. In this state their character is not altered from ruby 

 to blue by salt or acids ; they resist those chemical agents which are 

 resisted by gold, but are dissolved by chlorine, cyanides and the other 

 substances capable of acting on gold. Heated either in oxygen, 

 hydrogen, or air, no change of tint or quality is induced at such tem- 

 peratures as the paper can bear ; or, as far as can be judged, at any 

 higher temperature. 



