upon different Metals. ' 9 



EXPERIMENT XIII. 



I cast a square bar of tin, of similar dimensions to that which 

 I employed in Exp. ix. One half of its length was hammered 

 upon the edges till four new planes were formed in their places, 

 and the square reversed from its original position. Thus both 

 ends of the bar were still square, but the edges of one half were 

 in the direction of the planes of the other half, and a small 

 intermediate portion was irregularly octangular. The whole 

 was soaked in the shallow bath of mercury. The cleavage upon 

 the edges of the hammered half was perfect, and the trihedral 

 prisms and terminal pyramid very distinct. The edges of the 

 cast portion were not cleft, but the sharp divisions of the ham- 

 mered edges were continued down its faces, in ragged, irregular 

 cracks, which gaped particularly near the point of junction. 

 This end, therefore, had a tendency to separate into four tetra- 

 hedral prisms, and the force was so great, that they broke off 

 near the point of junction of the two parts of the bar, and 

 ultimately assumed the appearance represented at Fig. 5. The 

 sharp and even cleft upon one of the edges of the hammered 

 portion is exhibited at a, a, and the ragged crack upon the 

 corresponding face of the cast part at b b, gaping at the point 

 of fracture, c, c, as if rent asunder with great violence. 



I attempted in vain to produce analogous results with bars 

 of lead, brass, gold, silver, and zinc, for in none of these in- 

 stances could I obtain evidence of the action of any mechanical 

 force acting upon the particles of the metals ; although their 

 union with the mercury was, to all appearance, as intimate as 

 that of tin. No cracks or disruptions appeared in any of them. 

 The surfaces of the four first remained perfectly smooth and 

 continuous, but that of the last was corroded into cavities. 

 There can be little doubt, I think, that the disruptive force 

 which effected the disintegration of the tin bars, in the manner 

 above described, was the powerful contraction of the integrant 

 particles of the metal, in the act of combining with the mercury. 

 It has, indeed, been proved that the amalgam hence resulting 

 is of considerably greater density than the mean of its compo- 

 nent parts, and that such approximation of molecules must, 



