[BARNES] THE PHYSICAL CONSTANTS OF ICE 13 



Plasticity of Ice. 



Early observations of the plasticity of ice were made by Bianconi 

 in 1871. He caused rods and plates to be pressed into ice masses and, 

 by having various shaped holes in the plates, observed prisms of ice 

 issuing from these openings and bending over to meet the surface of the 

 plate. 



Pfaff, in 1875, made observations on the bending of ice bars. He 

 noticed that when the temperature was near zero a very small force pro- 

 duced permanent deformation. A bar, 1.3 cm. thick and 51 cm. long, 

 suspended with both ends free, bent in 24 hours about 2 mm. when the 

 temperature ranged between — 12° and — 3.5°C. With the temperature 

 between — 1° and 0°C., the bending was 9 mm. in the same time. 



Some very interesting experiments were carried out in 1885 by 

 Andrews, while engaged in measuring the conductivity and other phy- 

 sical properties of ice. He used a large ice block, on which he placed a 

 polished steel rod, 16 inches long by 0.292 inch in diameter. The rod 

 was made blunt at the end and rested under a weight of 181.5 pounds; 

 this served to press it into the ice at a rate depending on the hardness. 

 This experiment was carried out at different temperatures and the depth 

 to which the rod penetrated the ice under the varied conditions of tem- 

 perature, compared with the penetrability at 0°C., afforded a means of 

 calculating the relative hardness of the pure ice. He found that ice is 

 exceedingly hard from about — 40 °C. to about — 9°C., after which its 

 power of resistance rapidly decreases, giving way almost entirely at the 

 melting point, where it becomes relatively very soft and plastic. 



McConnell and Kidd in 1888, and McConnell alone in 1891, proved 

 the plasticity of ice under tension to be true. They showed that an or- 

 dinary bar of ice, composed of several crystals, will yield continuously 

 either to pressure or tension. They found, however, that a bar, cut from 

 a single crystal, with its length at right angles to the optic axis, showed 

 no signs of continuous stretching, even under half the breaking tension; 

 and this was also true of pressures, a crystal yielding in neither direction, 

 for forces applied at right angles to the optic axis. A single crystal of 

 ice has been termed by McConnell to be of perfect " brittleness." 



The e'cplanation offered by James Thomson, to account for the plas- 

 ticity of ice, in the light of what is termed regelation, that is, the melt- 

 ing of ice under pressure, and the water flowing to other parts of the 

 crystal to freeze again when relieved of the pressure, was found not to 

 accord with McConnell's experiments. This was especially so for his 

 experiments carried out at very low temperatures. 



