TABLE 58. SCALE OF MINERAL HARDNESS 



1. Talc 6. Feldspar 



2. Gypsum V. Quartz 



3. Calcite 8. Topaz 



4. Flourite 9. Corundum 



5. Apatite 10. Diamond 



The hardness of fresh ice at 0° is about 1. 5; according to Koch and Wegner at -15° it is 

 between 2 and 3, at -30° between 3 and 4, at -40° about 4, and finally, at -50°, fresh ice, according 

 to Heim, cannot be cut by a saw, that is, its hardness is near 6. 



The followirg observations by Badigin, conducted on the drift of the Sedou on 31 January 

 1938 during an air temperature near -40° is a characteristic example of the hardness of ice at low 

 air temperatures. 



"We saw a completely vertical wall of ice. We drew a circle (a 'bull's eye') and trained the 

 sights of our carbines on this target. The lead bullets flattened out leaving hardly noticeable marks 

 it proved that the ice was devilishly hard. " 



Burke considers that with the same temperature, the ice foimd at sea can be distributed in the 

 following order according to its hardness: 1) Icebergs and fragments of them; 2) many year-old 

 hummock ice; 3) "the tops" of hummocks formed by pressure; 4) one year old hummock ice; 5) thick 

 smooth fields and fragments of them; 6) thin fields and fragments of them; 7) nilas ice; 8) brash ice 

 and sludge. 



LITERATURE: 11, 23, 62, 77, 



Section 73. The Liquid State 



The transfer temperature of a body from one state to another and therefore also the temper- 

 ature of fusion, changes with a change of pressure according to Clayperon's following formula: 



At ^ a,„ — (Xi 



Ap £X ' 



where At is the change in the fusion temperature, 



AjD is the change in pressure, 



E is the mechanical equivalent of heat, 



T is the absolute temperature, 



a is the specific volume of pure water, 



a- is the specific volume of pure ice, 



\ is the heat of fusion. 



Since the specific volume of water is less than the specific volume of ice, consequently, the 

 freezing temperature decreases with an increase of pressure, in other words, the ice which has 

 been formed melts with an increase in pressure. 



182 



