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5
Stoffe. Dette er mindre end Halvdelen af, hvad
Forchhammer har fundet som Middeltal for Havets organiske
Bestanddele, men stemmer ganske godt overens meel nogle
Bestemmelser, der i clen senere Tid er udført af Professor
Almén1 i endel Vandprøver fra Omegnen af Spidsbergen.
Almén anvender hertil den samme Methode som ved
Drikkevand. idet han tilsætter Søvandet Svovlsyre og ved
gjentagne Kogninger med Kamæleon oxyderer, de organiske
Stoffe. Forat forhindre den skadelige Virkning af
Klor-metallerne fortynder han det iforveien med destilleret Vand.
Paa denne Maade linder han, at 100 Kc. Ishavsvand
indeholder 0.0018—0.0038 Gr. organiske Substantser.
Nordsøen, Skagerak og Kattegat skulde efter hans Undersøgelser
indeholde en større Mængde organiske Bestanddele, men
dog ikke saameget som det ferske Vand fra Floder og
Indsøer, hvilket viser, at Søvandet ikke fremfor dette er
begavet med nogen særegen reducerende Evne. Paa mange
af de fra Expeditionen medbragte Flasker havde der i
Tidens Løb udskilt sig et ubetydeligt fnokket Bundfald af
organiske Stoffe, eier under Mikroskopet viste sig at
indeholde Diatomeer. Filtratet forholdt sig imidlertid ganske
ordinært ligeoverfor- clen overmangansure Kali.
Til Bestemmelsen af Kalk, Magnesia og Svovlsyre i
Havvandet har jeg betjent mig af de almindelige
velbekjendte Methoder; men de forberedende Undersøgelser, jeg
har gjort forat forsikre mig om Paalideligheden af disse,
har vist mig, at de ikke altid giver saa nøiagtige og
overensstemmende Resultater, som ere nødvendige for et
Arbeide som det foreliggende, hvis man ikke i enkelte
Retninger tager nogle Forsigtighedsregler, der ere altfor løst
omtalte i de analytiske Haandbøger. Jeg vil derfor i det
følgende gaa lidt nærmere ind paa de fremgangsmaader,
jeg har brugt forat erholde de nøiagtigste Bestemmelser.
Kalk og Magnesia.
Til disse Bestemmelser afveiedes ’/.i Liter Søvand.
Efterat Magnesiaen ved Tilsætning af omtrent 25 Kc.
koncentreret Saltsyre og derpaa følgende Neutralisation med
koncentreret Ammoniakopløsning indtil et ubetydeligt
Overskud var forhindret fra at falde ud, blev Kalken i Kulden
bundfældt med et Overskud af oxalsur Ammoniak. Efter
en Nats Henstand frafiltreredes Bundfaldet, opløstes i varm
Saltsyre og udfældtes atter i Koghede med Ammoniak og
nogle Draaber oxalsur Ammoniak. Efter 12 Timers
Forløb blev Bundfaldet bragt paa Filtrum og bestemt som
Ætskalk. Tilstedeværelsen af Klornatrium har ingen
skadelig Indflydelse paa Kalkbestemmelsen, men synes
tvertimod at bidrage til en smuk krystallinsk Udfældning af den
oxalsure Kalk. Følgende Kontrolbestemmelser viser
Analysernes Paalidelighed:
organic matter. This is less indeed than half the
proportion Forchhammer gives as the mean for the organic
elements of ocean-water; it agrees, however, pretty closely
with certain determinations performed some time since by
Professor Almen1 with samples of sea-water collected in the
region of Spitzbergen. Almén resorts to the method adopted
for drinking-water, mixing sulphuric acid with the water,
in which, after repeated boiling with permanganate of
potash, the organic matter will be oxidized. To counteract
the injurious effect of the chlorides, he dilutes the samples
beforehand with distilled water. In this manner he finds
that 100" of Arctic sea-water contain from O.OU18’’1’ to
0.0038of organic matter. According to his observations,
the proportion is somewhat greater in the North Sea, the
Skagerak, and the Cattegat, though not equal to that in
the water of rivers and lakes, which shows that sea-water,
compared to the latter, cannot be possessed of any special
reductive property. In some of the phials brought home
with the Expedition, had formed a thin precipitate of
organic matter, which, when viewed under a microscope was
found to contain Diatoms. The filtered solution, however,
behaved as usual when treated with permanganate of
potash.
For determining the potash, magnesia, and sulphuric
acid in ocean-water, I have adopted the ordinary,
well-known methods; but the series of preliminary experiments
which I instituted with a view to test their trustworthiness,
has convinced me that they do not always give results
sufficiently accurate and congruous to warrant their adoption
here, unless indeed accompanied by certain precautions too
briefly dismissed in analytical class-books. I shall
therefore in the • context dwell more at large on the several
modes of operation by which I have sought to obtain the
most accurate determinations.
Lime and Magnesia.
For determining these substances, a quarter of a
litre of sea-water was first weighed. After guarding against
the precipitation of the magnesia, by adding about 25cc
of concentrated hydrochloric acid, and then neutralising
with a concentrated solution of ammonia, in slight surplus,
the lime was precipitated cold, by means of oxalate of
ammonia in excess. Next morning the precipitate was
filtered off, dissolved in warm hydrochloric acid, and again
precipitated, at the boiling point, with ammonia and a few
drops of oxalate of ammonia. After 12 hours, the solution
was filtered, and the precipitate weighed, as caustic lime.
The presence of chloride of sodium has no disturbing effect
on the lime-determinations; nay, it apparently contributes’
towards the beautiful crystalline precipitation of the oxalate
of lime. The following test-determinations vouch for the
accuracy of.the analyses: —
1 Svenska läkaresälskapets nya handlingar. Ser. II, del III,
Stockholm 1871.
1 Svenska läkaresälskapets nya handlingar. Ser. Il, del III,
Stockholm 1871.
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