32 Chemical and Physical Notes 



been formed. As the cold continues, more ice is formed out of the brine, 

 and the residual brine becomes more concentrated : but, however great 

 the cold, the surface layers of sea-water ice never acquire the hardness or 

 present the appearance of fresh-water ice. When the ice has acquired 

 a certain thickness, the formation of ice at the lower surface takes place 

 slowly, and the excluded brine disseminates itself at once in the water. 

 The ice, so formed, is much freer from salt than that which was first 

 formed on the water surface. The thicker the young ice becomes, the 

 less influence does the comparatively warm sea-water have on the upper 

 layers of the ice, and the lower does the temperature of the ice and the 

 entangled brine fall. 



" But as the brine is always -in contact with ice, it is always at its 

 freezing-point, which continually falls as the concentration of the brine 

 increases. By this continual freezing process of brine, which is always 

 getting more and more saturated, the liquid residue approaches more 

 and more the point where it can sustain the greatest cold without freezing. 

 On the surface there remains a very concentrated brine which keeps the 

 ice moist day after day, and which gives it its pastiness. On walking over 

 such a surfacfe, so long as no fresh snow has fallen on it, one is astonished 

 to find that every step one takes remains impressed on the white surface, 

 and it is difficult, especially for a new-comer, to understand how what he 

 takes for snow can be in a state of thaw at a temperature of 40 C., and 

 even lower. The moisture which collects in the foot-prints is, however, 

 not water but a very concentrated saline solution, principally chloride of 

 calcium, which in the course of time is absorbed into the ice. 



" From the above description of the process of formation of sea-water 

 ice, it is evident that when such ice is melted the saltness of the water 

 produced will vary according as the ice has been taken from the surface 

 layers or from lower down. 



"The following determinations were made. The water formed by 

 melting the white surface-ice which had taken thirty-six hours to form 

 under a cold of 33'5 C. had a specific gravity of I '087 ; and water 

 from ice which had taken sixty hours to form under a cold of 33 C. 

 had a specific gravity of 1-076, both measured at + 6'2 C. These 

 measurements correspond to a salinity of ir8 and lO'o per cent, re- 

 spectively. This ice was really the efflorescent surface skin. 



" The specific gravity of the water produced by melting the uppermost 

 5 centimetres of the above ice along with the white surface skin was 

 1-017 at +I97 C, that of the middle 9 centimetres was 1-009 a t + 1 1'4 C., 

 and that of the lowest 5 centimetres was roo8 at +i6'8C. These 

 specific gravities correspond to salinities of 2-5, 1-3 and i'2 per cent, 

 respectively. The average specific gravity of the sea-water is 1-025." 



Weyprecht assumed that the ice formed by freezing sea- 

 water was pure ice, and that its saltness was derived from 



