U-.^ 



80 



(-1^) 



+ 0.5 (t, — t). 



(1) 



By formula (1) Malgrem computed the table for the number of g-cal necessary to melt 1 g of 

 sea ice having different salinities and having temperatures equaling - 1° and - 2° at the starting 

 moment. These computations are continued for the lower temperatures (table 40). 



TABLE 40. THE NUMBER OF G-CAL NECESSARY TO MELT 1 G OF SEA ICE 



This table shows the basic difference between fresh and sea ice. Fresh ice demands a great 

 number of calories at the exact moment of its formation or melting, and a low number of calories 

 for changing its temperatures. Sea ice, on the contrary, demands a great number of calories for 

 changing its temperature and a low number at the exact moment of its melting. Thus, for instance, 

 80 g-cal are needed to melt one g of pure ice, and 2. 5 g-cal to raise its temperature from - 5° to 

 - 2°. In order to melt one g of sea ice of 15 o/oo salinity, only 17 g-cal are needed, but in order 

 to raise the temperature of this ice from - 5° to - 2°, it is necessary to expend 20 g-cal. This 

 is explained by the fact that fresh ice is formed at a constant freezing temperature, and with further 

 variations only its temperature changes. The process of forming sea ice continues steadily as long 

 as its temperature decreases. With changes in its temperature, constant melting alternates with 

 ice formation and vice versa. 



With the start of the intensified rise in spring temperature, the internal melting of sea ice 

 becomes constantly more intensive and at the moment of its decomposition, sea ice represents a, 

 so to say, mass destroyed from within ("rotten ice"), still preserving at times its external form 

 but easily destroyed by a slight warming or mechanical action. This explains the occasional ex- 

 tremely rapid disappearance of great masses of ice in the southern parts of the arctic basin during 

 the course of a polar summer, which creates the impression of "melting before one's eyes." 



LITERATURE: 52, 62, 73, 104. 



Section 62. The Coexistence of Water and Ice 



In investigating the question of equilibrium of the ice-water system, let us make the following 

 simplifying assumptions: 



1. The masses of water and ice participitating in the process are limited and protected from 

 the action of the atmosphere so that all changes that occur in the water or in the ice are conditioned 

 exclusively by their interactions. 



154 



