108 A TREATISE ON METAMORPHISM. 



than the other, may be far greater in the solution at high temperature than 

 would be calculated from the relative absolute temperatures of the solutions. 



Indeed, the velocity of a chemical reaction commonly increases 

 enormously with moderate increase of temperature. The partial explana- 

 tion of the phenomena lies in the fact that in most cases the reactions 

 themselves, as already seen, develop heat, which immediately reacts 

 to increase the kinetic energy of the remaining molecules, and this again 

 increases the kinetic energy of the molecules, and so on, there being 

 continual action and reaction between the chemical activity and the rising 

 temperature. 



Another illustration of the very important way in which increase of 

 temperature increases chemical action is the increased activity of substances 

 which at low temperatures are relatively inert. While at ordinary tempera- 

 tures carbon dioxide replaces silica in silicates, at temperatures of 100° C. 

 silica, if present in abundance, may replace carbon dioxide in carbonates." 

 While this is explained in part by the increase of activity of silicic acid 

 with increase of temperature, it doubtless in part is explained by the law 

 of mass action and the increased volatility of carbon dioxide at higher 

 temperatures. 



If the dissociation theory be true, a third factor which may have some 

 effect in producing speed of reaction with increase of temperature is the 

 increase in the amount of hydrolysis with increase of temperature. This is 

 illustrated by ferric chloride, which at low temperatures is regarded as but 

 little hydrolized, but at high temperatures is believed to be liydrolized to a 

 perceptible extent according to the equation: 

 Fe 2 Cl 6 +6H 2 0=Fe 2 ( OH ) 6 +6HCl. 



The presence of the ferric hydroxide is shown by the color of the solu- 

 tion. 6 In a similar manner, the carbonates and silicates are believed to be 

 hydrolized to a much greater extent at high temperatures than at low 

 temperatures. This is illustrated by calcium carbonate, which in solution 

 at high temperatures gives a strong alkaline reaction of calcium hydroxide, 

 and this is regarded as evidence of strong hydrolysis. It is possible that 

 hydrolysis is an important factor in the reactions which take place in the 

 different zones of metamorphism. 



«Bischof, Gustav, Elements of chemical and physical geology, translated by Paul and Drum- 

 mond, Harrison & Sons, London, vol. 1, 1854, p. 6. 



6 Ostwald, W., Grundlinien der anorganischen Chemie, Engelmann, Leipzig, 1900, p. 583. 



