346 HOW SALT ICE TURNS FRESH. 



But Dr. Rae thinks " the ice must have been formed 

 at least twelve months, or perhaps eighteen months" 

 before this change takes place, and his theory respect- 

 ing this remarkable phenomenon is as follows : 



" When the sea freezes, I do not think (he says) that the 

 saline matter assumes the solid state, unless the cold is very 

 intense, but that it remains fluid, in the state of very strong 

 brine, enclosed in minute cells. When the ice is raised above 

 the water level, the brine by its specific gravity, and prob- 

 ably by some solvent quality acting on the ice, gradually 

 drains off from the ice, and the small cells, by connecting with 

 one another downwards, become channels of drainage." * 



A small quantity of salt, placed upon ordinary lake 

 ice in situ, during a winter's frost at home, as anyone 

 will see who tries it, immediately begins to act ener- 

 getically upon it; the ice begins to crackle and soon 

 so far decomposes and becomes eaten away, that it 

 gets quite rotten and dangerous to stand on, and the 

 salt finally seems to pass through it, and escapes into 

 the water below, f 



Great icebergs are generally, we believe, found to 

 consist of fresh water ice. Captain Parry for instance 

 tells us that these " ice islands are frequently composed 

 of pure fresh water ice, which is found in pools on the 

 surface, or running down the sides " (during the summer 

 time) "and watering in this manner is a general 

 practice of ships in icy seas." 



Some of these great bergs, or 'ice islands' are often of 

 enormous size, not uncommonly rising from 100 to 300 

 feet above the surface of the seas, and having a circum- 



* Dr. I. Rae on " The Physical Properties of Ice, " p. 650. 

 f Result of experiments with salt on lake ice in sitit. 

 Narrative of an Attempt to Reach the North Pole in Boats, by Capt. 

 W. E. Parry, in 1827 quoted in Roper's Navigation, p. 368. 



