130 Proceedings of Royal Society of Edinburgh. [mar. 21, 
whether ice so formed does or does not contain salt, experiment 
would at once give a decisive answer. Yet, relying on experiment 
alone, competent authorities have given contradictory answers. All 
agree that ice, whether formed artificially in the laboratory by 
freezing sea-water, or found in nature as one of the varieties of sea- 
water ice, retains, in one form or another, and with great tenacity, 
some of the salt existing in solution in the water. The question at 
issue is whether this salt is to be attributed to the solid matter of 
the ice or to the liquor mechanically adhering to it, from "which it 
is impossible to free it. Most bodies, and especially those which 
take a crystalline form, are easily purified and freed from all 
suspected foreign matter, with a view to analysis, by the simple 
operation of washing and drying. It is impossible to wash the 
crystals, formed by freezing a saline solution, with distilled water, 
because they melt at a temperature below that at which distilled 
water freezes. The effect of the addition of a small quantity of 
distilled water to a quantity of saline ice is at first the anomalous 
one, that what was a wet sludge is transformed into a dry crystal- 
line powder. It is, of course, impossible to dry the ice by heat, 
and to do so by more intense freezing would be begging the question. 
The experimental difficulties therefore account for some of the 
divergence of opinion on the subject. The mixed character of the 
substances examined has also much to do with it. As a rule, it may 
be said that those investigators who have confined their observations 
to the laboratory have concluded that the ice forming when saline 
solutions of moderate concentration, including sea-water, are frozen, 
is pure ice, and the salt from which it is impossible to free it entirely 
belongs to the mother-liquor, while those who have collected and 
examined sea-water ice in high latitudes have come to the opposite 
conclusion. 
During the Antarctic cruise of the “Challenger” I made a number 
of observation on the sea- water ice found in those regions, and, re- 
lying principally on the fact that the melting temperature of the ice 
was markedly lower than that of fresh-water ice, and that it w T as 
impossible by any of the ordinary means familiar to chemists for 
freeing crystals from adhering mother-liquor to materially reduce its 
salinity, I came to the conclusion that the ice forming in freezing 
sea- water is not a mixture of pure ice and brine, but that it contains 
