302 Scientific Proceedings, Royal Dublin Society. 
particulars additive. In solutions of electrolytes, which may, 
perhaps, be looked upon as chemically similar to glasses, viscous 
properties, and many others, are additive.’ 
According to the theory I advocate here, the silicate, A, con- 
taining a small quantity of silica, crystallizes out at a higher 
temperature than the silicate, B, containing a larger percentage of 
silica, because the crystallizing point of A is less affected by the 
silica than in the case of B. A test of the melting point under 
ordinary conditions may not reveal this, for the rigidity of B, due to 
its greater amount of silica, may confer apparent solidity upon it at 
a temperature at which A has yielded to gravitational and surface 
tension forces. ‘This will be understood from the diagram below. 
Fluidity 
Temperature 800° 2 1187° 14.00° 
Here, at the level, 4 7, the fluidity has attained to such a 
degree as to cause yielding to gravitational distortion. This 
occurs at a lower temperature for the augite than for the quartz. 
According to the hypothesis now put forward, approaching the 
1 The elaborate work ‘‘ On the Relations between the Viscosity (Internal Friction) 
of Liquids and their Chemical Nature,’’ by Messrs. Thorpe and Rodger (Phil. Trans., 
vol. 185 A, p. 397, and vol. 189, p. 71), applies to very definite chemical compounds, 
but even in these cases many interesting regularities are described by the authors. 
See Whetham’s ‘‘ Solution and Electrolysis’? (Cambridge, 1895), chap. xz. 
