1908] Ice and its Natural History. 243 



WEEKLY EVENING MEETING, 



Friday, May 8, 1908. 



Sir William Crookes, D.Sc. F.R.S., Honorary Secretary and 

 Vice-President, in the Chair. 



John Young Buchanan, Esq., M.A. F.R.S. 3I.R.I. 



Ice and its Natural History. 



In a single lecture it will be impossible for me to do more than deal 

 with those points in the natural history of ice which have come under 

 my own notice, and which I have made the subject of special in- 

 vestigation. 



The Nature of tlie Ice formed Inj Freezing Saline Solutions. — 

 During the Antarctic cruise of the " Challenger," the old question 

 arose as to wliether the salt which is always found in the water pro- 

 duced by melting sea ice, was present in the solid state as part of the 

 crystalline ice, or in the liquid state as part of the adhering brine. 

 It was one of considerable economical importance to whalers and other 

 mariners who frequent Polar seas. It had been found that freshly 

 frozen genuine sea-water ice was not drinkable. Genuine land ice, 

 which is easily recognised, gave, of course, good water. The great 

 mass, however, of the ice found floating in Polar seas is of mixed 

 origin. Thus, in its first stage it may be the ice formed by the 

 primary freezing of sea -water. On this falls snow. When there is 

 wind the sea breaks on the edge of the floating ice and throws salt 

 spray over it, which freezes in due time. Hence a piece of sea ice, 

 picked up at random, is likely to be a very heterogeneous substance ; 

 and no two pieces can be expected to behave exactly alike. It is, 

 therefore, not surprising that the reports of different navigators 

 regarding the potability of the water formed by melting sea ice 

 differed. Some maintained that it was undrinkable ; others held that 

 it could be drunk, if the first portions melted were rejected, and only 

 the last fraction used. 



In February 1874, when the "Challenger" reached her furthest 

 south, much ice of all kinds was met with, and I took the opportunity 

 to make a study of the floating sea ice. I collected many samples, 

 observed their melting temperatures, and determined the percentage 

 of chlorine in the water produced by their fusion. The results ob- 

 tained showed that their melting temperature was very variable, and 

 always below 0° C. It was further observed that this temperature 

 was the lower the greater the percentage of chlorine found in the 



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