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A negative value in the above table means that the volume increases 

 with decreasing temperature. The expansion of pure water on form- 

 ing ice at 32° F. is equivalent to a coefficient of expansion of —900 in 

 the units of the table. 



The annual course of temperature in the pack ice of the East Sibe- 

 rian Sea, from measurements made in the Maud from 1922 to 1924, 

 is given in the following table : 



TEMPERATURE IN THE SEA ICE, °F. 



SPECIFIC GRAVITY 



As indicated in discussing the thermal expansion of ice, the specific 

 gravity of pure ice is about nine-tenths that of water at the freezing 

 point. The exact value for water is 0.9921 at 32° F., and for pure 

 ice 0.9168. Sea ice will contain a proportion both of salt or brine, 

 which will increase the specific gravity, and of air, which will reduce 

 the specific gravity. Malmgi-en found extreme values of 0.924 for 

 newly formed ice, and 0.857 for the top of summered ice, in which 

 the brine cells were replaced with air bubbles. He found that in 

 general sea ice less than one year old had a specific gravity greater 

 than 0.90, but that it fell below 0.90 after the ice had weathered a 

 summer. 



Glacier ice. such as makes up icebergs, has a fairly high apparent 

 air content ; but it is likely that the air is under considerable pressure 



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