0.000169 = 0.091 ^ ^ , 



(7) 



Actually, if the coefficient of thermal expansion changes sign, then obviously, the minimum 

 density would occur when that coefficient would equal 0. Thus, from formula (6) we obtain 



where S-: is the salinity of sea ice, 



5^ is the salinity of the brine in the salt cell at temperature t, 



° T is the change of the salinity with temperature changes. 

 6t 



6 S ^ 

 As we have seen, the values S and— r — ^determine the temperature of sea ice. Therefore 



T 6 T 



using formula (7) it is not difficult to compute such a temperature 6' for any salinity of sea ice at 

 which the density of sea ice will be a minimum (table 47). 



TABLE 47. THE MINIMUM DENSITY TEMPERATURE OF SEA 

 ICE OF DIFFERENT SALINITIES 



Nevertheless, it should be pointed out that the figures in this table are more of a theoretical 

 interest, inasmuch as the changes in the density of sea ice in connection with the change in its 

 temperature as we have seen are comparatively slight. 



LITERATURE: 44, 62, 77. 



Section 66. Density as a Function of Porosity 



The ratio between the volume of air or gas bubbles found in ice to the total volume of ice is 

 called the porosity of ice and is expressed in percentage. Arnold- Aliabev calls the following 

 value the coefficient of porosity. 



n S„ — S 



1— n 



where n is the porosity of ice 



6 is the density of ice devoid of air bubbles. 



The bubbles in sea ice can be of different origin and form. A part of the bubbles forms as 

 a result of the separation of gases dissolved in water which had not succeeded in leaving the cells 

 between the crystals of ice during ice formation. As has been confirmed by experiments with arti- 

 ficial freezing, the amount of these bubbles is proportional to the saturation of the water with gases 



165 



