]()() 



.\s to the t'acliKiI ()l)s('i'\';i1 ions llicy can |)i'ol)al)]y he recon- 

 ciled i r 1 lie teiiiix'i'al ui'es at which crystalli/at ion was found 

 to 1)0 conij)lete, according' to the first principle, are ]jre- 

 C'isely the teniix'ratures at which the crystals cease to .i>i'OAv, 

 accordiiii*' to the second. The first i)riiiciple sliould then 

 be abandoned since the facts alleg-edly ex])laiiied by it are 

 really consequences of the other ])i-inciple. 



IV. THE FROZEN STATE 

 PROPERTIES OF ICE AND OF FROZEN SYSTEMS 



A historical and critical review of the investigations on 

 the physical constants of ice, and a large bibliography, Avill 

 be found in H. T. Barnes' Book "Ice Engineering" (1928). 

 The subject having thus been reviewed, we shall merely 

 mention the essential established data, indicate the use that 

 the biologists have made of them and suggest some other 

 applications. Most of our information is obtained from 

 Barnes' work. 



1. Mechanical Properties of Ice. The plasticity of ice 

 is well exemplified in the movement of the glaciers; ice 

 really flows. The velocity of flow depends on the tempera- 

 ture and on the pressure exerted and it is relatively high 

 in large masses of ice, such as the glaciers (for figures, see 

 H. Hess: "Die Gletscher" 1904). 



Andrews (1885) studied ice deformability at different 

 temperatures by measuring the degree of penetration of a 

 steel rod applied to blocks of ice. He found that the resis- 

 tance to penetration varied little when the temperature 

 was raised from - 40° to - 9° but decreased rapidly from 

 -9° to 0°. This considerable plasticity at a few degrees 

 below the melting point is probably the cause of the trans- 

 formation of the ice pattern observed by Luyet and Gibbs 

 (1937) in frozen epidermal cells of plants (Fig. 26). 



The flow of ice does not seem to result, as it is usually 

 thought, from a partial melting followed l)y recrystalliza- 

 tion, but it consists probably in a sliding of the crystalline 

 planes one over the other (McOonnell, 1891). In some 

 other crystalline materials, gliding lines can occasionally 



