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17
til i Middel 34.96 og for det i 1878 undersøgte mellem
7Ude og 80de Breddegrad beliggende Strøg til 35.64 °/0.
Fuldstændigt tilsvarende er det af Buchanan fundet at
være paa den sydlige Halvkugle, idet Surstofprocenten i
Overfladen der varierer fra omkring 33 i Æqvåtoregnene
til ca. 35 omkring den sydlige Polarcirkel.
Dette lod med temmelig stor Bestemthed formode,
at de for destilleret Vand gjældende, af Bunsen opstillede,
Absorbtionscoefficienter ikke skulde være gyldige for Søvand,
idet det. naar Overfladevandsluftens Sammensætning fandtes
at variere med Bredden, maatte være det Naturligste at
skrive disse Variationer paa Temperaturforandringerne. Det
vil imidlertid ikke føre til noget rimeligt Resultat, om man
vil betragte Temperaturen som den Variable og af de her
foreliggende Observationer forsøge at udlede en Lov for
Absorbtionscoefficienternes Variationer med Temperaturen.
Man vil "da finde, at de enkelte Observationer staa ikke
ubetydeligt i Strid med hinanden, idet der for
Surstof-mængdernes Vedkommende overalt optræder meget større
Afvigelser, end man kan antage begrundede i
Observations-feil. Det kun (le dog ikke synes tilraadeligt at lade det
bero hermed og forsøge at discutere de foreliggende
Observationer uden nøiere Kjendskab til
Absorbtionscoefficienternes Afhængighed af Temperaturen, og jeg besluttede
derfor at bestemme saavel Sammensætning som Mængde af
den i Søvandet ved forskjellige Temperaturer opløste Luft.
Først gjordes en Del Forsøg, hvorved Søvandet i et
Bad af constant Temperatur søgtes mættet ved flere Timers
Grjenneifiledning af Luft, (saaledes som Bunsen har gaaet
frem ved sine Bestemmelser1), hvorefter den opløste Luft
uddreves og analyseredes paa den før beskrevne Maade.
De paa denne Maade mættede Vandprøver afgave
bestandig Luftmængder, som uden Hensyn til den Temperatur,
hvorved Vandet var mættet, viste nogenlunde nær den
samme Sammensætning (med 34.9 °/o Surstof mod 65.1 °/0
Kvælstof), medens de ofte temmelig stærkt afvigende Tal,
som udtrykte de absolute Mængder af opløste Gaser,
tydeligt . viste.. at der paa denne Maade ikke var opnaaet
fuldstændig Mætning.
Professor Waage foreslog mig derfor at gjentage disse
Forsøg med nogen Variation i den Maade, hvorpaa
Mætningen iværksattes, og har jeg som Følge deraf ved de
senere Forsøg benyttet følgende Fremgangsmaade. En
passende Portion Søvand af nogenlunde høi Egenvægt rystedes
med Luft i en rummelig Kolbe i et Tidsrum fra 1 til 2
Timer under stadig Vexlen af den i Kolben værende Luft
og hensattes derpaa i nogle Timer ganske rolig, idet
Temperaturen saavel under Rystningen som senere holdtes
fuldstændig constant. Forat overbevise mig om, at jeg har
opnaaet fuldstændig Mætning, har jeg nærmet mig Mæt-
Norwegian Expedition in 1876 and 1877. amounts to 34.96.
and for that lying between the 70th and 80th parallels of
latitude, to 35.64 per cent. Buchanan observed precisely
the same phenomenon in the southern hemisphere, the
proportion of oxygen varying from about 33 per cent in
the Equatorial Seas to about 35 per cent in the vicinity of
the Antarctic Circle.
Reasoning on these data, there were strong grounds
to assume, that the coefficients of absorption given by
Bunsen for distilled water could not apply to sea-water:
for. the composition of the air in surface-water having been
found to vary with the latitude, the most probable cause
of this phenomenon would seem to be temperature.
Meanwhile, Ave shall not arrive at a satisfactory result by
regarding temperature as the variable factor, and by
seeking from the observations here set forth to discover a
law according to wliich the coefficients of absorption
vary with the temperature. The individual observations
would in that case be found to clash, inasmuch as the
variation with regard to oxygen is invariably greater
than can be assumed to arise from errors of observation.
However, it did not seem advisable to leave the. question
as it stood, and proceed to the discussion of the results
without having further investigated the relation of the
coefficients of absorption to the temperature: and I resolved,
therefore, on determining alike the composition and the amount
of the air absorbed by sea-water at different temperatures.
A series of experiments were first instituted with
a view to saturate sea-water with air. viz. by placing
it in a bath of constant temperature, and for the space
of several hours uninterruptedly conducting through it a
current of air. — the mode of operation adopted by
Bunsen for his determinations.1 — after which the air
absorbed in the water was driven off. and analysed by the
process previously described. The samples of water
saturated in this manner invariably yielded quantities of air
which, irrespective of the temperature at which the water
had been saturated, were found to be very nearly
uniform in composition, viz. 34.9 per cent oxygen and 65.1 per
cent nitrogen, whereas the figures, often widely divergent,
expressing the absolute quantities of the gaseous bodies
absorbed, gave sufficient proof that by this method complete
saturation had not been attained.
At Professor "Waage’s suggestion. I repeated these
experiments, varying slightly the means by which
saturation was sought to be effected, and have since .adopted the
following mode of operation. A quantity of sea-water, of
considerable specific gravity, is shaken, along with air. in
a roomy matrass for one or two hours, the air in the
matrass being frequently renewed, and then left perfectly
still for a few hours, at the precise temperature preserved
during its continual agitation. To be quite sure that I have
really succeeded in saturating the water. I approach the
point of saturation as it were from opposite directions:
1 Bunsen, (rasom. Methoden — 16."».
Den norske Nordhavsexpeditioii. Toruoe: Chemi.
1 Bunsen. Gasom. Methoden, p. 105.
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