494 JOHN JOHNSTON AND PAUL NIGGLI 
The augites were considerably ‘‘uralitized” (transformed into 
fibrous hornblende, appearing as pseudomorphs of the augite), the 
process being accompanied by a marked change of composition. 
This interpretation of the process presupposes equilibrium condi- 
tions; but whether equilibrium conditions obtained or not, this 
example may serve to point out the possibility of the actual occur- 
rence of such differences. 
Closely related to the phenomena of transformation of mix- 
crystals is the phenomenon of allotropy, according to the latest 
views, which so far are the only views which aid us materially in 
correlating this property with other properties of the substance. 
The phenomenon of allotropy.—It is well known that wherever a 
substance exhibits polymorphism, its various allotropic modifica- 
tions may be obtained from a solution or fusion merely by varying 
the conditions of crystallization (e.g., rate of cooling, concentration 
of solvent). On this fact as foundation, a theory of allotropy has 
been developed by Smits,’ the basic idea of which is that the differ- 
ent modifications are in reality all present in equilibrium with one 
another in the solution, the appearance of any one form in the solid 
state being determined by the conditions of this internal equilib- 
rium, the position of which in turn is affected specifically by the 
solvent medium. 
Let us consider, for the sake of simplicity of statement, that no 
foreign solvent is present, that the liquid phase is a melt of the pure 
substance. Such a liquid phase, which hitherto has been generally 
supposed to be unary (containing only a single molecular species), 
is considered by Smits to be pseudo-unary; that is, it contains two 
(or more) pseudo-components in mutual equilibrium. As a neces- 
sary consequence of the internal equilibrium in the liquid phase it 
follows that there is equilibrium in the solid phase between the same 
pseudo-components; the position of this equilibrium is, of course, 
not identical with that of the equilibrium in the liquid phase (just 
as in the case of mix-crystals). In other words, when an apparently 
unary liquid solidifies, even although the cooling goes on in such a 
way that equilibrium between the pseudo-components obtains con- 
tinuously, the solid phase separating out is not a pure pseudo- 
component but is itself a pseudo-unary system in internal equilib- 
tA. Smits, Z. physik. Chem., LX XVI (1011), 421, and later papers in 1912 and 
1913, especially zbid., LX XXII (1913), 657. 
