32 R. W. Wood, Jr. — Effects of Pressure on Ice. 



Even under this enormous pressure the ice was found to 

 have had sufficient viscosity to support the weight of the shot. 



The maximum depth of the ice in the glacial epoch never 

 exceeded two miles and such a mass would yield a pressure of 

 about two tons to the inch, or two hundred and sixty-six (266) 

 atmospheres. Sir William Thomson's experiments show that 

 the melting point of ice is lowered .0075° C. for every atmo- 

 sphere of pressure, that is to say, a mass of ice subjected to 

 pressure has its temperature lowered .0075° C. for every addi- 

 tional fifteen pounds to the inch. Let us now consider exactly 

 what the effect of a pressure of 266 atmospheres will be : the 

 reduction of temperature will of course be "0075° X 266, or 

 — two degrees Centigrade (more exactly 1-955° C). Starting 

 with water at 0° we shall then have a mass of ice and water 

 at a temperature of — two degrees Centigrade. To determine 

 the amount of ice melted or reduced to a state of pressure- 

 molten water, we make use of the well-known formula, 

 _ temperature (in —degrees) 

 X ~ ~ ^79^25 



x being a fractional quantity representing the proportion of 

 ice liquefied, and the constant quantity 79-25 being the latent 

 heat of fusion for ice. The result is fa, this being the exact 

 amount of ice that will be liquefied by a pressure of 266 atmo- 

 spheres. The condition of a lower layer of a mass of ice two 

 miles thick will be as follows. The temperature will be —2° 

 Centigrade, and a certain portion, namely fa, will be in the 

 state of pressure-molten water, which, being diffused through 

 the mass of the ice, will not sensibly diminish its rigidity. 



It will be seen that the pressure of such a mass of ice was 

 considerably less than that required to cause ice at the melting 

 point to flow easily and rapidly through a small orifice. It 

 may be argued that the time element has not been considered. 

 Time has nothing to do with the result, except as heat is fed 

 to the bottom layer from the earth. Insulate the mass from 

 all sources of heat, and the equilibrium will remain unchanged 

 until the end of time. The law of conservation of energy 

 decrees that this must be so. 



It is true that glacial ice was not thus insulated : that it 

 received heat from the earth we all admit, but let us consider 

 exactly what the effect of this heat supply was. We have at 

 the beginning a temperature of —2° C., and fa of the ice in 

 a liquid state. Heat is fed from the earth which tends to 

 raise the temperature, but the constant pressure keeps this 

 uniform, and the heat is expended in melting more ice. After 

 a lapse of time we shall have a considerable portion of the ice 

 in a liquid state, but by considering carefully the conditions, 

 we shall see that it is therm o-molten and not pressure-molten. 



