54 FREEZING OF SALT WATER. Chap. IV. 



series of experiments upon the freezing of salt water ; I will 

 here briefly state the process he found necessary, in order to 

 procure fresh water from sea ice. 



Finding that sea ice contained less salt than the sea water, 

 he collected and thawed a considerable quantity of it ; he 

 then exposed it in tubs until coated over with half-inch ice ; 

 he gathered this second crop of ice, thawed it, and found 

 that it also was less salt than the water which produced it. 

 Again repeating the process of exposure in tubs, he obtained 

 a third crop of ice, which was found to yield drinkable 

 water ; and repeating this process a fourth time, a small 

 quantity of nearly pure fresh water was obtained. 



He found that the ice would contain less salt when frozen 

 slowly than when exposed to a very low temperature, and 

 therefore rapidly frozen. 



A very beautiful frosty efflorescence appears upon sea ice 

 when formed at low temperatures in calm weather, it is in 

 fact a portion of the brine expressed by the action of 

 freezing. 



No wonder, then, that sledge dogs, when driven hard over 

 this ice, which soon cuts their feet, suffer intense pain, often 

 falling down in fits ; nor that snow thinly covering such ice 

 wholly or partially thaws so frequently, even when the 

 temperature is far below the freezing point. Should it then 

 rise to near the freezing point, the young ice, thus coated 

 with sludge so saline as to resist the ordinary freezing 

 temperature, not unfrequently becomes so weakened, as to be 

 unsafe. l 



29M. — Keen, biting, N.W. winds. No cracks in the ice, 



1 In a paper read before the Royal Geographical Society on 12th April, 

 1869, from Captain Montgomery of the Indian Survey, it is stated, that 

 at the gold diggings in Thibet, first visited by our explorers in 1867, 

 it is the custom of the miners to use melted ice for drinking, as the water 

 is too salt ! These mines are at an elevation of 16,300 feet, and the 

 cold is very considerable. 



