342 Intelligence and Miscellaneous Articles. 



Professor Henry suggested that the silver, instead of evaporating, 

 merely sunk into the pores of the copper, and that by carefully re- 

 moving the surface of the latter by the action of an acid, the silver 

 would reappear. To verify this by experiment, Mr. Cornelius heated 

 one end of a piece of thick plated copper to nearly the melting-point 

 of the metal ; the silver at this end disappeared, and when the metal 

 was cleaned by a solution of dilute sulphuric acid, the end which had 

 been heated presented a uniform surface of copper, whilst the other 

 end exhibited its proper coating of silver. The unsilvered end of the 

 plate was next placed, for a few minutes, in a solution of muriate of 

 zinc, by which the exterior surface of copper was removed, and the 

 surface of silver was again exposed. This method of recovering the 

 silver before the process of plating silver by galvanism came into use, 

 would have been of much value to manufacturers of plated ware, 

 since it often happened that articles were spoiled, in the process of 

 soldering, by heating them to the degiee at which silver disappears. 



It is well-known to the jeweller, that articles of copper, plated with 

 gold, lose their brilliancy after a time, and that this can be restored 

 by boiling them in ammonia ; this effect is probably produced by the 

 ammonia acting on the copper, and dissolving off its surface, so as 

 to expose the gold, which, by diffusion, has entered into the copper. 



A slow diffusion of one metal through another probably takes 

 place in cases of alloys. Silver coins, after having lain long in the 

 earth, have been found covered with a salt of copper. This may be 

 explained by supposing that the alloy of copper, at the surface of the 

 coin, enters into combination with the carbonic acid of the soil, and 

 being thus removed, its place is supplied by a diffusion from within ; 

 and in this way it is not improbable that a considerable portion of 

 the alloy may be exhausted in the process of time, and the purity of 

 the coin be considerably increased. 



Perhaps, also, the phenomenon of what is called segregation, or 

 the formation of nodules of flint in masses of carbonated lime, and of 

 indurated marl in beds of clay, may be explained on the same prin- 

 ciple. In breaking up these masses, it is almost always observed, 

 that a piece of shell or some extraneous matter occupies the middle, 

 and probably formed the nucleus, around which the matter was accu- 

 mulated by attraction. The difficulty consists in explaining how the 

 attraction of cohesion, which becomes insensible at sensible distances, 

 should produce this effect. To explain this, let us suppose two sub- 

 stances uniformly diffused through each other by a slight mutual at- 

 traction, as in the case of a lump of sugar dissolved in a large quan- 

 tity of water, every particle of the water will attract to itself its pro- 

 portion of the sugar, and the whole will be in a state of equilibrium. 

 If the diffusion at its commencement had been assisted by heat, and 

 this cause of the separation of the homogeneous particles no longer 

 existed, the diffusion might be one of unstable equilibrium ; and the 

 slightest extraneous force, such as the attraction of a minute piece 

 of shell, might serve to disturb the quiescence, and draw to itself the 

 diffused particles which were immediately contiguous to it. This 

 would leave a vacuum of the atoms around the attracting mass : for 

 example, as in the case of the sugar, there would be a portion of the 



