1857.] Relations of Gold to LighL 445 



This deposit transmits various coloured rays : some parts are grey, 

 others green or amethystine, or even a bright ruby. In order to 

 remove any possibility of a compound of gold, as an oxide, being 

 present, the deflagrations were made upon topaz, mica, and rock 

 crystal, as well as glass, and also in atmospheres of carbonic acid 

 and of hydrogen. Still the results were the same, and ruby gold 

 appeared in one case as much as in another. Being heated, all 

 parts of the deposit became of an amethystine or ruby colour ; 

 and by pressure these parts could be changed so as to transmit the. 

 •green ray. 



The production of fluids^ consisting of very finely divided par- 

 ticles of gold diffused through water, was spoken of before. These 

 fluids may be of various colours by transmitted light from ruby to 

 blue ; the effects being produced only by diffused particles of 

 metallic gold. If a drop of solution of phosphorus in bisulphide 

 of carbon b^ put into a bottle containing a quart or more of very 

 weak solution of gold, and the whole be agitated, the change is 

 brought about sooner than by the process formerly described ; or if 

 a solution of phosphorus in ether be employed, very quickly indeed ; 

 so that a few hours' standing completes the action. All the prepa- 

 rations have the same qualities as those before described. The 

 differently coloured fluids may have the coloured particles par- 

 tially removed by filtration ; and so long as the particles are kept 

 by the filter from aggregation, they preserve their ruby or other 

 colour unchanged, even though salt be present. If fine isinglass 

 be soaked in water, then warmed to melt it, and one of these rich 

 fluids be added, with agitation, a ruby jelly fluid will be obtained, 

 which, when sufficiently concentrated and cold, supplies a tremu- 

 lous jelly ; and this, when dried, yields a hard ruby gelatine^ which 

 being soaked in water, becomes tremulous again, and by heat and 

 more water yields a ruby fluid. The dry hard ruby jelly is per- 

 fectly analogous to the well known ruby glass, though often finer in 

 colour ; and both owe the colour to particles of metallic gold. 

 Animal membranes may in like manner have ruby particles diffused 

 through them, and then are perfectly analogous in their action on 

 light to the gold ruby glass, and from the same cause. 



When a leaf of beaten gold is held obliquely across a ray of 

 common light, it polarizes a portion of it ; and the light transmitted 

 is polarized in the same direction as that transmitted by a bundle of 

 thin plates of glass ; the effect is produced by the heated leaf as 

 well as by the green leaf, and does not appear to be due to any 

 condition brought on by the heating or to internal strncture. When 

 a polarized ray is employed, and the inclined leaf held across it, the 

 ray is affected, and a part passes the analyzer, provided the gold 

 film is inclined in a plane forming an angle of 45** with the plane 

 of polarization. Like effects are produced by the films of gold pro- 

 duced from solution and phosphorus, and also by the deposited 

 dust of gold due to the electric discharge. The same effects are 



