Chemical and Physical Notes 33 



brine mechanically adhering to it, from which it was impossible 

 to free it. There was no experimental evidence to prove this. 

 Others thought that, as the ice formed by freezing salt water 

 has a different melting-point from fresh-water ice, and it 

 is impossible by melting it to produce water free from salt, 

 the salt is an essential constituent of the ice. Experiments 

 made by the writer 1 in the Antarctic area during the cruise of 

 the " Challenger," supported the latter view, and he held it 

 until subsequent experiments 2 , which he made some twelve 

 years later, enabled him to supply direct experimental evidence 

 that the contrary is the case, that the ice-crystals are indeed 

 pure ice, and that their saltness is due only to adhering brine 

 from which it is impossible to free them. 



Demonstration that the Ice produced by Freezing Sea-water 

 and similar Solutions is pure Ice. The principle guiding the 

 research was, that if the ice, which forms when sea-water or 

 a saline solution of similar concentration is partially frozen is 

 pure ice, then pure ice of independent origin such as snow, 

 must, when mixed with the sea-water or saline solution, melt 

 at the same temperature as the ice which is formed by 

 freezing the solution, when the concentration is the same. 

 Sea-water and various saline solutions were experimented 

 with on these lines, and the following was the scheme of 

 experiment : 



The solution of a salt, for instance, chloride of sodium, 

 was gradually cooled in a freezing mixture, and the tempera- 

 ture watched as more and more crystals separated out ; at 

 suitable intervals the temperature was accurately noted, and 

 simultaneously a sample of the brine was taken ; in this way 

 a series of freezing temperatures ^, t 2 , t 3 , etc., was obtained, 

 and after analysis of the samples a corresponding series of 

 salinities s lt s 2 , s 3 , etc., was obtained. When the lowest 

 temperature, say t 6 , was obtained, the salinity was s s ; then 

 the vessel containing the solution was removed from the 

 freezing mixture, and it was exposed to the heat of the air of 



1 ' On Sea-water Ice.' Proc. K. S. (1874), vol. xxii. p. 431. 



2 'On Ice and Brines,' by J. Y. Buchanan (1887). Proc. R. S. E., vol. xiv. 

 p. 129; also Nature,\o\. xxxv.pp-5i6, 608, and vol. xxxvi. p. 9. (Below, p. 130.) 



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