26b GREENLAND or polar ice. 



solidity by exposure to the sun and air, and arc 

 commonly fresh, whilst those pieces taken out of 

 the sea are somewhat salt. Although it is very 

 probable, that this retention of salt may arise from 

 the sea-water contained in its pores, yet I have 

 never been able to obtain, from the water of the 

 ocean, by experiment, an ice either compact, 

 transparent, or fresh. That the sea- water has a 

 tendency to produce fresh ice, however, is proved 

 from the concentration observed in a quantity ex- 

 posed in an open vessel to a low temperature, by 

 the separation of the salt from the crystals of ice, 

 in the progress of the freezing. Thus it is, that 

 in the coldest weather, wheri a ship exposed to a 

 tempestwous sea, is \y ashed with repeated sprays, 

 and thereby covered with ice, that in different 

 places obstructing the efflux of the water over- 

 board, a portion always remains unfrozen, and 

 which, on being tasted, is found tq contain salt 

 highly concentrated. This arises from the freez- 

 ing point of water falling in a certain ratio ac- 

 cording to the degree of saltness ; thus, though 

 pure water, of specific gravity 1.0000, freeze with 

 a temperature of 32°, water of specific gravity 

 1.0263, containing about 5^oz. (avoird.) of salt 

 in every gallon of 231 cubic inches, that is, with 

 the degree of saltness common to the Greenland 

 Seas, freezes at 28^°. Sea-water concentrated by 

 freezing, until it obtains the specific gravity of 

 irlP45, requires a temperature of 13j° for it^ 



