FUSION AND SOLIDIFICATION 73 



etc. When, instead of a single metal, traces of 

 others are present, the lines of separation between 

 the primary crystals are much emphasised, and, 

 when the quantity of other substances Is consider- 

 able, there arise the complicated structures, which 

 we shall presently study under the head of alloys. 



The process of the freezing of sea-water under 

 the Influence of the Intense cold of an Arctic 

 climate Is an interesting example of the applica- 

 tion of the same principles. The phenomena 

 have been described by the explorer, Weyprecht, 

 whose account Is quoted by Mr J. Y. Buchanan 

 In his *' Chemical and Physical Notes." When 

 a new surface of sea- water Is exposed to the cold 

 air, In a short time the surface of the water 

 begins to get thick, threads like a spider's web 

 runnlnor out from the old ice. Brine is entano^led 

 in this structure, and its concentration constantly 

 becomes greater as the quantity of Ice increases. 

 At this stage the ice Is a pasty mass, and follows 

 every motion of the water on which it floats. 

 With a temperature of —40^ C. the new Ice, even 

 after twelve hours, is still so soft that, in spite 

 of Its thickness, a stick can easily be thrust 

 through it. 



As soon as a layer of Ice is formed over the 

 surface, the cooling of the underlying water pro- 

 ceeds much more slowly, and less salt is entangled 

 in the crystals. The lower layers of sea-water 

 ice give therefore, when melted, a much fresher 

 water than can be obtained from the upper layers. 

 Even when strong enough to walk on, the surface 

 of new sea-Ice, frozen by air at — 40, Is still 

 moist and soft, the residual liquid consisting of 

 a concentrated solution of various salts, chiefly 



