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centage of sulphuric acid is greater at the surface of the sea than
at the bottom.
I think the theory »on salt solutions and attached water»
published in 1875 by Prof. Guthrie will best account for the
observations enumerated above. Prof. Guthrie found, that
every diluted salt solution, on being cooled sufficiently, yields
up ice, until its temperature reaches a certain point peculiar
to the salt, when it solidifies as a whole, maintaining
throughout that constant temperature. The proportion of water
relatively to the salt in these »cryohydrates» is ordinarily
very large and makes the molecular formulae given to these
combinations appear somewhat exuberant to the chemist.
This must have induced a short-sighted critic to overlook the
importance of the discovery of Mr. Guthrie, which still
affords the only starting-point for an acceptable theory of the
origin of the sea-ice.
»Bearing in mind the existence of the cryohydrates,
certainly of sulphate of magnesium and doubtless also of chloride
of calcium (?), at temperatures not far below 0° C, a rapid fall
of temperature may be accompanied by more complex
phenomena of gelation; for if the ice be quickly removed from a
large mass of water by freezing, the resulting brine may easily
be so enriched, as to throw out one or more cryohydrates,
which thus perpetuate in situ a definite amount of saline
matter The saltness of a floe depends not only upon its
age but also upon the rapidity, with which it was at first
formed and upon the lowest temperature, to which it has
subsequently been exposed.»
We will leave the question of the appropriate chemical
formula of the cryohydrates aside and listen to some simple
facts, told us by Prof. Guthrie, about the freezing points and
the chemical composition of some of the cryohydrates, which
can possibly arise from the freezing of sea-water.
The cryohydrate of
contains
solidifies at
NaCl
KaCl
Ca Cl.
Mg S04
Na, S04
76.39 % water
— 22° C
8O.00 %
72.00 %
78.14 %
95.45 % »
— 11°.4 C
— 37°. 0 C
— 5°.o C
— 0°.7 C
According to this table we ought to expect, that the
cryohydrate of NaoS04
4.55 % of Na2S04 + 95.45 % of H>0
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