VKGA-EXVEDITIOSKNS V AT KN S K A F f. IG A A II II ET KK. 30] 



ine) occasions no great discrepancy in the behavior of the 

 liqiiid water IV from that of pure water. In the solid state 

 however, the differenee is verv consiilerable. 



CIIAPTEPv 5. 



Chemical changes in the composition of water 

 caused by freezing. 



From the preceding chapters the reader must have discov- 

 ered the weighty influence, which the saltness of the ice, 

 however slight it be, has upon its physical properties. I hope, 

 it will appear from this exposition, that the composition of 

 the sea-ice is a subject of such importance, that it ought to 

 attract the attention of the chemists as well as tlie physicists 

 raore and more. For my part I confess, that I write this 

 ■chapter more in the hope of winning the interest of m}^ 

 readcrs for the following questions than from any hope I have 

 of being able to give a conclusive answer to them myself. 



Is the salt a constant and normal component of the sea-ice? 

 Mr. F. Guthrie tried to decide this question by artificial 

 freezing of sea-water from Dover. The ice, which formed 

 freely from the sea-water, contained about *l:, of tlie usual 

 percentage of salt, but a part of it, which had been pressed 

 between linen and flannel in a screw-press, was found to hold 

 only ^/i5- Guthrie observes, »that the almost undiminished 

 •saltness of the unpressed ice is due, as suggested by Dr. 

 Rae, to the entanglement amidst the ice-crystals of a brine 

 richer in solid constituents than the original water itself. 

 Such brine, which is here squeezed out in the press, drains 

 in nature clown from the upper surface of the ice-fioe by gra- 

 vitation and also is replaced by osmic action by new sea- 

 water, which again yields up fresh ice, so that, while new 

 floes are porous and salt, old ones are more compact and 

 niuch fresher, as the traveller ol)served>. All other observers, 

 except Dr. Buchanan,^ agree in the opinion, that the saltness 

 of the sea-ice is due to the entan2:lemcnt of salt brine in the 



» Proc. R. S. XXIV, p. 011. 



