Dr. J. Rae on some Physical Properties of Ice. 57 



being already saturated, can hold in solution no more salt than 

 it already contains. 



Could not salt be obtained readily and cheaply by this means 

 from sea-water in cold climates ? 



During several long journeys on the Arctic coast, in the early 

 spring before any thaw had taken place, the only water to be 

 obtained was by melting snow or ice. By experience I found 

 that a kettleful of water could be obtained by thawing ice with 

 a much less expenditure of fuel, and in a shorter time, than 

 was required to obtain a similar quantity of water by thawing 

 snow. Now, as we had to carry our fuel with us, this saving of 

 fuel and of time was an important consideration, and we always 

 endeavoured to get ice for this purpose. We had another in- 

 ducement to test the sea-ice frequently as to its freshness or 

 the reverse. 



I presume that almost every one knows that to eat snow 

 when it is very cold, tends to increase thirst, whereas a piece of 

 ice in the mouth is refreshing and beneficial, however cold it 

 may be ; we were consequently always glad to get a bit of fresh 

 ice whilst at the laborious work of hauling our heavy sledges ; 

 yet with these strong inducements we were never able to find 

 sea-ice, in situ*, either eatable when solid or drinkable when 

 thawed, it being invariably much too salt. The only exception 

 (if it may be called one) to this rule, was when we found rough 

 ice, which, from its wasted appearance and irregular form, had 

 evidently been the formation of a previous winter. This old 

 ice, if projecting a foot or two above the water-level, was almost 

 invariably fresh, and, when thawed, gave excellent drinking- 

 water. It may be said that these pieces of fresh ice were frag- 

 ments of glaciers or icebergs ; but this could not be so, as they 

 were found where neither glaciers nor icebergs are ever seen. 



How is this to be accounted for ? Unfortunately I have only 

 a theory to offer in explanation. 



When the sea freezes by the abstraction of heat from its 

 surface, I do not think that the saline matter, although retained 

 in and incorporated with the ice, assumes the solid state, unless 

 the cold is very intense, but that it remains fluid in the form of 

 a very strong brine enclosed in very minute cells. So long as 

 the ice continues to float at the same level, or nearly the same 

 level, as the sea, this brine remains ; but when the ice is raised 

 a little above the water-level, the brine, by its greater specific 

 gravity, and probably by some solvent quality acting on the ice, 

 gradually drains off from the ice so raised; and the small cells, 



* What I mean by ice in situ is ice lying flat and unbroken on the 

 sea, as formed during the winter it is formed in. 



