462 0. D. von Engeln — Studies on Ice Structure. 



has been suggested that the liquid phase consists of a mixture 

 of ice molecules (H 6 3 ) and water molecules (H 4 2 V Similarly 

 it is quite possible that a residuum of water molecules exists 

 in the solid phase, ice, at temperatures below, but near 

 the freezing point. As the change from the liquid phase, 

 water, to the solid phase, ice, is accompanied by expansion it 

 follows that compression of the ice will result in the lowering 

 of its melting point. Under uniform pressure this has been 

 experimentally determined to amount to •00722°C. per atmos- 

 phere of pressure. Johnston and Adams * contend that what 

 is ordinarily termed the compression of solids is resolvable into 

 uniform pressure and shearing stress. They further insist 

 that permanent deformation of crystalline aggregates results 

 from the effects of non-uniform pressure or shearing stress 

 and that such deformation is occasioned by the real melting of 

 those particles that at any instant bear the brunt of the load. 

 On this basis they assert that non-uniform pressure lowers 

 the melting point of ice '09°C. per atmosphere of pressure. 

 Considered in connection with the possibility of a residuum of 

 water molecules in ice at temperatures near the freezing point 

 this concept of the nature of compression effects on solids 

 suggests the probability of a considerable volume of water 

 being evolved by moderate pressure on ice at or near the freez- 

 ing point temperature and such an effect has been noted by 

 Hess f in exact experimental studies. 



Ice masses do not consist of single crystals but, as shown 

 above, of aggregates of comparatively small units variously 

 oriented. The resistance of such masses to deforming stresses 

 would appear to be due to three factors : (a) the nature of the inter- 

 locking of the units, (b) the molecular cohesion of the ultimate 

 particles of a unit crystal, (c) the molecular cohesion existing 

 at the contact of adjacent crystal faces. It follows that 

 experimental studies of ice under compression with reference 

 to glacial phenomena should be directed toward ascertaining 

 the behavior of ice as a crystalline aggregate rather than to 

 the investigation of the physical properties of unit crystals. 



That there is a very considerable difference between the 

 value of molecular cohesion of the particles of a unit ice 

 crystal and that between particles of adjacent crystal faces is 

 indicated by the differences in crushing strength exhibited by 

 the pond ice put under compression (a) with principal axes of 

 the component prisms parallel to the pressure direction and (b) 

 normal to it, the crushing strength in the second case being 



* Johnston, J., and Adams, L. H. : On the Effect of High Pressures on 

 the Physical and Chemical Behavior of Solids, this Journal, xxxv, 205, 

 March, 1913. 



fHess, H. : Uber die Plastizitat des Eises, Annalen der Physik, (4), xxxvi, 

 j>p. 449-492, 1911. 



