The seepage of brine through ice in the course of time is caused by many reasons. In this 

 connection, the force of gravity works first of all (inasmuch as the density of brine is greater than 

 the density of the ice and the water under the ice). The force of gravity in the narrow capillaries is 

 somewhat balanced by the rise of the level in them due to surface tension. However, inasmuch as 

 in the course of time the upper parts of the ice rise constantly higher above sea level as long as the 

 ice continues to grow, and inasmuch as the size of the capillaries also increase with the course of 

 time, finally the force of gravity, especially in the upper ice layers, begins to overcome the molec- 

 ular forces. 



Whitman focused attention on the displacement of the salt droplets encased in ice which causes 

 the vertical gradient of temperature in ice by its presence. 



As we have seen, salt cell brine concentration is determined by the temperature of the ice 

 layer In which a given cell is located. In the presence of a vertical temperature gradient, the brine 

 concentration will be higher on the warmer side of the cell and it will be lower than the concentra- 

 tions necessary for conditions of equilibrium on the colder side. Hence the ice will melt on the 

 warmer side of the cell and thus lower the brine concentration, while new ice will be formed on the 

 colder side, and thus it will raise the brine concentration. As a result of these processes, a drop 

 of brine will be displaced from the colder ice layers to the warmer ones during which the concen- 

 tration of the brine in the drop will decrease simultaneously. 



Whitman confirmed his reasoning by experiments with 3.31 o/oo concentrations of table salt 

 solutions, artificially frozen in special cylindrical test tubes. These test tubes were maintained for 

 some time at constant temperatures at both their upper and lower ends and then the brine concen- 

 tration was determined. The results, as an average of five experiments, are given in table 35. 



TABLE 35. THE CHANGE IN TABLE SALT CONTENT WITH A 

 CHANGE IN TEMPERATURE GRADIENT 



The length of the experiment in hours 



The temperature in the upper part of the test tube in C 



o 



The temperature in the lower part of the test tube in C 

 Table salt content in o/oo: 



in the upper layer 



in the 2nd layer 



in the 3rd layer 



in the 4th layer 



in the bottom layer 



It is seen from the table how rapidly the displacement of the brine occurs . 



Very low temperatures at the upper ice surface, and close to the temperature of freezing at 

 the lower ice surface are observed in sea ice during the winter. Therefore, the phenomenon noted 

 by Whitman should cause energetic drainage of the brine downward during the winter. During the 

 summer, the coldest temperatures are found in the middle parts of the ice and the salt drops should 

 therefore move up and down (figure 54). But during the summer, the capillaries and cells contain- 

 ing the brine are constantly increased in size at the ice surface, the ice becomes very porous, and 

 the force of gravity begins to play a leading role in brine seepage. Due to this, the ice becomes 

 only slightly salty. 



146 



