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II. "Ice Observations." By DAVID WALKER, M.D., Surgeon 

 and Naturalist to the Arctic Discovery Expedition. Com- 

 municated by THOMAS ANDREWS, M.D. Received De- 

 cember 16, 1858. 



(Abstract.) 



The contradictory statements of Dr. Sutherland and Dr. Kane, with 

 regard to the saltness of the ice formed from sea-water, the former 

 maintaining that sea-water ice contains about one-fourth of the salt 

 of the original water; the latter, that if the cold be sufficiently 

 intense, there will be formed from sea-water a fresh and purer ele- 

 ment fit for domestic use, induced the author to take advantage of 

 his position, as naturalist to the expedition now in the northern seas, 

 to reinvestigate the subject. 



The changes which he has observed sea- water to undergo in 

 freezing are the following. When the temperature falls below 

 + 28*5, it becomes covered with a thin pellicle of ice ; after some 

 time this pellicle becomes thicker and presents a vertically striated 

 structure, similar to that of the ordinary cakes of sal-ammoniac. 

 As the ice further increases in thickness, it becomes more compact, 

 but the lowest portion still retains the striated structure. On the 

 surface of the ice, saline crystals, designated by the author " efflo- 

 rescence," soon begin to form, at first few in number and widely 

 separated, but gradually forming into tufts and ultimately covering 

 the whole surface. At first, the increase in thickness of the ice is 

 rapid, but afterwards the rate of growth is much slower and more 

 uniform. The ice formed yields, on being melted, a solution differ- 

 ing in specific gravity according to the temperature at the time of 

 congelation, its density being less, the lower the temperature at 

 which the process of congelation took place. Although the author's 

 observations extended from + 28*5 to 42, he was never able to 

 obtain fresh-water from sea-ice, the purest specimen being of specific 

 gravity 1*005, and affording abundant evidence of the presence of 

 salts, especially of chloride of sodium, in such quantity as to render 

 it unfit for domestic purposes. 



The efflorescence already referred to appeared sooner or later, 

 according to the temperature of the air, but generally commenced 

 when the ice was f of an inch thick, and continued to form till 



