440 



A TREATISE ON METAMOEPHISM. 



CHANGE FROM WATER TO ICE. 



When water changes to ice it expands 9 per cent. According to 

 Dewar, the decrease in the freezing* temperature of water corresponding 

 to an increase of pressure of one atmosphere up to 700 atmospheres is 

 0.0072° C. per atmosphere. It follows from this that in order to prevent 

 the change from water to ice taking place at temperatures below 0° C 

 very great pressures must be exerted. These pressures are shown by the 

 following table : 



Pressures required to keep water liquid at temperatures below 0° C a . 



It follows that where water is in rocks and the temperature is below 

 0° C, in general the rocks are not strong enough to resist the change of 

 the water to ice; therefore an expansion of 9 per cent takes place. When 

 this expansion occurs one of two things happens. The water obtains the 

 additional space by pushing aside the material of the soil or rock or by 

 expanding into opening's not fully occupied by the water. The latter is 

 especially likely to occur in rocks in which the water is that of imbibition 

 and which therefore are not saturated. 



In such cases the space between the particles of the rocks, as, for 

 instance, grains of soil or grains of sand in a sandstone, is so great that 

 the expansion of freezing need not move the grains with reference to one 

 another. In general it may be said that, in proportion as the rocks approach 

 saturation, disruption is likely to occur; in proportion as the amount 

 of contained water becomes small, disruption is not likely to take plaoe. 



« See Mousson, A., Einige Thatsachen betreffend das Schmelzen und Gefrieren des Wassers: Ann. 

 der Physik und Chemie, J. C. Poggendorff, vol. 105, Leipzig, 1858, p. 161. 



