GNEISSES IN THE HIGHLANDS OF NEW JERSEY 695 



contained large amounts of water. Nevertheless the property of 

 critical temperatures of liquids appears at times to be somewhat 

 of an obstacle to a clear comprehension of the miscibility of rock 

 magma with water and other volatile substances at a high tem- 

 perature. The critical phenomena seem sometimes to be under- 

 stood to imply that at temperatures above 374° C. water, under all 

 circumstances, ceases to be a liquid and becomes a gas. A better 

 statement would be that at the critical temperature and at the 

 corresponding pressure the properties of liquid and vapor cease to 

 differ. The discontinuity of properties which characterizes the 

 transformation from liquid to vapor at lower temperatures and 

 pressures disappears. Moreover, the critical temperature of a 

 liquid is not a fixed point but varies with the amount of material 

 in solution. With pure water the critical phenomena appear at 

 374° C, but when water holds material in solution the vapor 

 pressure is lowered and the critical point is raised. The greater 

 the amount of dissolved material the greater is the displacement. 



These facts have been emphasized in an investigation recently 

 carried out by G. W. Morey^ in the Geophysical Laboratory, of 

 which the results have just been published. In one experiment 

 2 gm. of a glass of the composition K2O: i . 7 Si02 was heated with 

 4.842 gm. water to a temperature of about 360° in a gold crucible 

 within a gas-tight steel bomb. The result was a pasty glass con- 

 taining 32 per cent water. In another experiment 2 gm. of glass 

 of the same composition as before and 5 gm. water were exposed 

 to a temperature of 490° under the same conditions. The product 

 obtained was a hard glass containing 20 per cent water.^ In 

 the latter experiment the temperature was far below that at which 

 the dry materials would begin to melt and at the same time more 

 than 100° above the critical temperature of water alone, and the 

 formation of a strongly hydrated glass is a striking phenomenon. 



There is, therefore, no~ theoretical difficulty in supposing that 

 fused silicates may form a homogeneous solution with water and 

 other volatile substances at high temperatures, and the properties 



"G. W. Morey, Jour. Amer. Chem. Soc, XXXVI, 2 (1914), 215-30. 

 ^Evidence was obtained which showed that even those glasses which became 

 highly rigid when cooled formed mobile liquids at the temperature of the experiments. 



