222 Johnston and Adams — High Pressures on the 



The possibility of accounting for the now of solids by means 

 of this conception of a true local melting produced by unequal 

 pressure was considered by Tammann,* but rejected by him 

 on what appear to the writers to be insufficient grounds. He 

 was unable to detect any discontinuity in the rate of flow of 

 ice at the pressure calculated by means of the equation for 

 the lowering of equilibrium temperature by unequal pressure, 

 and hence was led to doubt the thermodynamic admissibility 

 of the derivation of this formula. To reason from this lack of 

 discontinuity that the effect of unequal pressure upon the 

 melting point is illusory, might be justifiable if Tammann had 

 been dealing with a single crystal ; but dealing as he was with 

 an aggregate of crystals, flow began w T henever the pressure 

 on any one of them exceeded the melting pressure under the 

 particular conditions. Indeed the behavior of ice in this 

 respect is precisely similar to that of the metals — a fact specific- 

 ally noted by Tammann himself — the only difference being 

 that the absolute values of the pressure are lower than for the 

 common metals. 



Tammann concludes :f "From the work on the velocity of 

 flow of crystalline substances it follows that the flow is not con- 

 ditioned by a previous melting, but that the plasticity, the 

 reciprocal of the viscosity, is a property characteristic of the 

 substance." In order to account for the fact that the velocity 

 of flow, and hence the "plasticity," of ice increases very 

 considerably with the pressure, it must be assumed that its 

 viscosity diminishes greatly with pressure. This assumption 

 may hold, for water at low temperatures and low pressures is 

 an exception to the general rule that the viscosity of liquids is 

 increased by pressure ;J to the writers, nevertheless, it seems 

 less forced to account for the flow by the aid of the considera- 

 tions advanced in this paper; namely, that flow is the result of 

 a partial melting. On this basis we can readily see why 

 increased pressure, which causes more ice to melt and hence 

 increases the amount of water present, should increase the 

 plasticity. Moreover, so far as we have been able to ascertain, 

 this explanation conflicts with none of the recorded observa- 

 tions on the flow either of ice of any other substance. Indeed, 

 it receives direct confirmation from some recently published 

 work of Hess on the plasticity of ice§ : he found, as Tammann 

 previously had also observed, that at a given temperature a 

 considerable movement of the plunger takes place under a 

 pressure much lower than that deduced thermodynamically 



* Ann. Phys. (4), vii, 198, 1902 ; Krystallisieren und Schmelzen (Leipzig 

 1903). pp. 173-181. 

 t Loc. cit. 



JR. Cohen, Ann. Phys., xlv, 666, 1892 ; Hauser, ibid., v, 597, 1901. 

 §Ann. Phys., xxxvi, 449-93, 1911. 



