S Mr. Daniell on the Action of Mercury 



them, and they were left in nearly a dry state. The tube was 

 dissolved away at its lower end to a thin edge, and the action 

 of the mercury had evidently decreased as it ascended : the 

 upper part to which the crystals were attached was but little 

 acted upon, so that, in its whole length, it gradually tapered 

 downwards. The substance of the metal, even above the part 

 immersed, was saturated with mercury, and had become very 

 brittle. 



Hence it appears that the action of the mercury upon the 

 alloy was, first to saturate its pores and disintegrate its sub- 

 stance, forming a brittle, uncrystallized compound which it 

 must have subsequently dissolved. The amalgam thus pro- 

 duced, being of less specific gravity than the fluid metal, floated 

 to its surface, where the attraction of cohesion between the par- 

 ticles of the compound, being greater than the attraction which 

 held them in solution in the fluid, caused them to crystallize. 

 I have formerly * remarked, that if a mass of any soluble salt 

 be carefully suspended in water, it will be more acted upon at 

 its upper than its lower end, and will assume, more or less, the 

 form of a cone, with the apex at the surface of the liquid. The 

 particles of water which are in immediate contact with the 

 salt, combine with a portion of it, and thus becoming speci- 

 fically heavier than the remainder, sink to the bottom of the 

 vessel ; others succeed and follow the same course. A layer 

 of saturated solution is thus deposited, which increases in 

 depth as the process advances, protecting in its rise that part 

 of the mass which is covered with it from further action. In 

 the present instance the process is directly the reverse : the 

 solvent, by union with the solid, becomes specifically lighter, 

 and the saturated solution is first formed upon the surface ; and 

 the action continuing longest at the bottom of the mass, a cone 

 is produced with its apex downwards. 



EXPERIMENT IT. 



A piece of pure tin, in the usual form of closely- aggregated 

 imperfect prisms, in which it is found in commerce, was partly 

 immersed in mercury, and left undisturbed for a month. Upon 



* Journal of the Royal Institution, vol. i,, p. 24, 1st Series, 



