1888.] Prof. Liveing, On Solution and Crystallization. 223 
or angle, the tensions will have a resultant of sensible magnitude 
in some direction falling within the angle. Whenever all the 
faces of a crystallographic form are developed every such resultant 
will be met by an equal and opposite resultant and the form will 
be one of equilibrium. If one edge, or angle, be modified, the 
opposite edge, or angle, must either be similarly modified, or the 
resultant arismg from the modification must be equilibrated by 
some internal forces produced by displacement of the molecules. 
In general equilibrium is attained by similar modifications of 
similar edges and angles, but when only some of the edges or 
angles of a crystal are modified while other similar edges or 
angles are not modified we usually have evidence of the con- 
sequent internal strain. Thus cubes of sodium chlorate which 
have half the angles truncated by faces of a tetrahedron rotate 
the plane of polarised light, hemihedral tourmalines are pyro- 
electric and so on. This theory therefore accounts for the plane 
faces of crystals, the law of indices, the most common combina- 
tions, and the cleavages. The same theory accounts for the 
development of plane faces when a crystalline solid of any shape 
is slowly acted on by a solvent. Solution will proceed so long as 
the entropy of the system is increased by the change, but when 
the solution is nearly saturated there will be an increase of entropy 
from the solution of a surface which has more than the minimum 
surface energy while there will be no increase from the solution of 
a surface which has only the minimum energy. 
(2) On the effect of an electric current on saturated solutions. 
By C. Curez, M.A., King’s College. 
The following experiments were undertaken at the suggestion 
of Prof. J. J. Thomson, to whom I am much indebted for sugges- 
tions as to the salts employed and the method of carrying on the 
operations, which were conducted in the Cavendish Laboratory. 
It has been shown by Prof. Thomson, from considerations based 
on a generalized form of Lagrange’s equations, that a species of 
reciprocity may be expected in the interaction of natural agencies. 
Thus as the electrical resistance of a solution depends on the 
quantity of salt present, it seems desirable to know what effect 
the presence of an electric current has on the quantity of salt in 
solution. 
It is obvious that the current will have an indirect effect 
owing to its heating the solution. The application of heat in 
general accelerates the rate of solution in an unsaturated solution, 
and by raising the point of saturation enables more salt to dissolve 
