GREENLAND OR POLAR ICE. 



269 



congelation, having its freezing point reduced 

 i 8y* below that of pure water ; and water satu- 

 rated with sea-salt remains liquid, at a tempera- 

 ture of — 4°. 



Thus, we are presented with a natural process 

 for extracting salt from the sea, at least for great- 

 ly facilitating that process in a concentration of 

 the saline particles, by the agency of frost. 



When salt-water ice floats in the sea at a freezing 

 temperature, the proportion above, to that below 

 the surface, is as 1 to 4 nearly ; and in fresh water^ 

 at the freezing point, as 10 to 69, or 1 to 7 nearly. 

 Hence, its specific gravity appears to be about 0.873. 

 Of this description is dW young ice, as it is called, 

 which forms a considerable proportion of packed 

 and drift ice in general ; where it occurs in flat 

 pieces commonly covered with snow, of various 

 dimensions, but seldom exceeding fifty yards in 

 diameter. 



Fresh-Water Ice. 



Fresh-water ice^ is distinguished by its black 

 appearance when floating in the sea, and its beau- 

 tiful green hue and transparency when removed 

 into the air. Large pieces may occasionally be 

 obtained, possessing a degree of purity and trans- 

 parency, equal to that of the finest glass, or most 

 beautiful crystal ; but generally, its transparency 



