CHEMICAL AND PHYSICAL NOTES. 77 
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 sur- 
face 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 concen- 
trated brine which keeps the ice moist day after day, and which gives 
it its pastiness. On walking over such a surface, 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 how- 
ever, 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., has a specific gravity of 1-087; 
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 11:8 
and 10:0 per cent. respectively. This ice was really the efflorescent 
surface skin. 
“The specific gravity of the water produced by melting the upper- 
most 5 centimetres of the above ice along with the white surface 
skin was 1:017 at +19°-7, that of the middle 9 centimetres was 
1:009 at +11°°4C., and that of the lowest 5 centimetres was 1°'008 
