1 857.] of Gold (and other Metals) to Light. 421 



they are obtained. But that the blue particles are always 

 merely larger particles does not seem admissible for a moment, 

 inasmuch as violet or blue fluids may be obtained in which the 

 particles will remain in suspension as long as in the ruby fluids ; 

 there is probably some physical change in the condition of the 

 particles, caused by the presence of the salt and such affecting 

 media, which is not a change of the gold as gold, but rather a 

 change of the relation of the surface of the particles to the 

 surrounding medium. 



When salt is added in such quantity as to produce its effect 

 in a short time, it is seen that the gold reflexion of the particles 

 is quickly diminished, so that either as a general turbidness or 

 by the cone of rays it becomes less visible ; at last the metal 

 contracts into masses, which are comparatively so few and 

 separate, that when shaken up in the fluid, they confer little 

 or no colour or character, either by reflected or transmitted 

 light. In these cases no re-solution of the metal is effected, 

 for neither the salt nor hydrochloric acid, when used in like 

 manner, has any power to redissolve the gold. The same 

 aggregating effect is shown with all the fluids whatever their 

 colour, and also with the deposits that settle down from them. 

 When salt is added to the solution of gold before the phos- 

 phorus, and therefore before the reduction of the gold, the 

 fluid first produced is always ruby ; but it becomes violet, purple, 

 or blue, with a facility in proportion to the quantity of salt 

 present. If that be but small, the ruby will remain for many 

 days unchanged in colour, and the violet-ruby for many weeks, 

 before the gold will be deposited, the degree of dilution or 

 concentration always having its own particular effect, as before 

 described; the more finely divided preparations, i. e. the ruby 

 and amethystine, appear to be more permanent than when the 

 salt is added after the separation of the gold. 



Many other bodies besides salt have like action on the par- 

 ticles of gold. A ruby fluid is changed to or towards blue by 

 solutions of chlorides of calcium, strontium, manganese ; sul- 

 phates of magnesia, manganese, lime ; nitrates of potassa, soda, 

 baryta, magnesia, manganese ; acetates of potassa, soda, and 

 lime ; these effect the change freely : the sulphate of soda, 

 phosphates of soda and potassa, chlorate of potassa, and acetate 

 of ammonia acted feebly. Sulphuric and hydrochloric acids 



