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Kalk1. Dette Bundfald viste sig at bestaa af Magnesia
foruden en Smule Jern og Fosforsyre og neppe mærkelige
Spor af Kulsyre. Inddamper man derimod en Liter
Søvand til dens halve Volum, saa danner eier sig et Bundfald,
som bestaar af kulsur Kalk og Gibs og kun indeholder
smaa Mængder Magnesia. Men hvorvidt den kulsure Kalk,
som i dette Tilfælde udskiller sig. virkelig fra Begyndelsen
af har været opløst som saadan i Søvandet, kan naturligvis
ikke afgjøres ved dette Forsøg. Tvertimod synes det med
megen Kimelighed at fremgaa af Hr. Tornøe’s
Undersøgelser over Kulsyren i Søvandet, at denne fortrinsvis maa
være bundet til Natron som dobbelt kulsurt Salt.
Ved videre Inddampning af Søvandet udskilles Gips
og. Klornatrium. Endnu efterat Hovedmassen af Kogsaltet
har afsat sig, indeholder Moderluden alle de Kali- og
Mag-nesiåsalte, der fra Begyndelsen af har været tilstede i
Vandet. I en saadan Moderlud fra 20 Liter Søvand •
lykkedes det mig at paavise Jod efter den af
Koetstorfer-angivne Methode. Ved Afkjøling under 0" udskilte den
Krystaller af svovlsurt Natron, ved høiere Temperatur
svovlsur Magnesia.
Forchhammer angiver i sin Afhandling 0111 Søvandet,
at han flere Gange har fundet Svovlvandstof i de
hjemsendte Prøver. Han tilføier imidlertid, at denne
Forbindelse muligens kan være opstaaet ved en mindre
omhyggelig Rensning af Flaskerne; men i enkelte Tilfælde føler
han sig dog forvisset om, at den maa have dannet sig af
Søvandets egne Bestanddele. Jeg har aldrig kunnet
opdage den karakteristiske Lugt af denne Gas ved Aabningen
af de fra Expeditionen medbragte Vandprøver. Selv nogle
af disse, der undtagelsesvis vare blevne opbevarede i
almindelige, med Korkpropper forsynede, Flasker og først
aabnedes efter et Par Aars Forløb, befandtes at være
fuldkommen lugtfrie.
Efter Forchhammers Mening skulde Svovlvandstoffet
have dannet sig ved Oxydation af de organiske Stoffe paa de
svovlsure Saltes Bekostning. Forat bestemme Søvandets
organiske Bestanddele benyttede Forchhammer Kogning med
Kamæleon, og indførte derved en Methode, der som
bekjendt senere har faaet en udstrakt Anvendelse meel
Hensyn til Drikkevand.
Han tilsatte Søvandet saameget af en bekjendt
Opløsning af overmangansur Kali, at det efter et Opkog og
Henstand i 12 Timer beholdt en rødlig Farve. Den i
. Overskud tilsatte Kamæleon fandtes ved at besteinme den
Mængde af denne, der var nødvendig forat frembringe
samme Farve i det samme Volumen rent Vand. Ved at
anvende denne Methode har jeg fundet, ;it 100 Kc. Søvand
ialmindelighed affarver 0.0005 Gr. overmangansur Kali,
hvad der omtrent skulde svare til 0.0025 pCt. organiske
1 Sammenlign Tornøe’s Afhandling om Kulsyren i Søvandet.
- Zoitschrif’t fiir anal. Chemie, 1878, S. 305.
failed however to detect the slightest trace of lime.1 The
said deposit was found to consist of magnesia, along with a
little iron and phosphoric acid, and hardly appreciable traces
of carbonic acid. If, on the other hand, a litre of
sea-water be reduced by boiling to half its volume, the
precipitate will consist of carbonate of lime and gypsum, the
proportion of magnesia being comparatively small. But
whether the carbonate of lime precipitated in this case was
originally present as such in the water, is a question which
cannot be decided by this experiment. Judging, however,
from the results of Mr. Tornøe’s observations on the
carbonic acid present in sea-water, that gas may with good
reason be inferred to occur chiefly in combination with
soda as a bicarbonate.
On further evaporation of the sea-water, gypsum and
chloride of sodium are deposited; and even after the bulk
of the chloride of sodium has been precipitated, the
mother-liquor contains all the salts of potash and magnesia
originally present in the water. In mother-liquor of
this description, obtained from 20 litres of sea-water, I
succeeded in detecting iodine, by the process described
by Koetstorfer.2 On reducing the temperature,
sulphate of soda was deposited; on raising it, sulphate of
magnesia.
In the treatise on ocean-water, Forchhammer records
his having frequently met with hydrosulphuric acid in the
samples of sea-water sent liim: and this compound may. lie
thinks, in most cases, be traced to impurities in the bottles;
though in some lie feels convinced it had formed from the
constituent parts of the sea-water itself. I did not
however in any case detect the fætid smell characteristic of
that gas, when opening the numerous phials brought home
with the Expedition. Certain of the samples even
exceptionally preserved in common corked bottles, and allowed
to stand over for the space of two years, proved to be
quite inodorous.
According to Forchhammer, hydrosulphuric acid is
formed by the oxidation of organic matter, at the cost of
the sulphates. In order to determine the organic elements
of sea-water, Forchhammer boiled the latter with
permanganate of potash, thus devising a process which has since
been extensively adopted for the determination of organic
matter in drinking-water.
He added to the sea-water a solution of
permanganate of potash, of known strength, sufficient to give it, on
being boiled and suffered to stand over for the space of
12 hours, a reddish colour. The excess of permanganate
of potash was found by determining the proportion of that
substance necessary to produce the same colour in an equal
volume of pure water. Adopting this method, I found
that 100"* generally sufficed to discolour 0.0005gr of
permanganate of potash, which nearly corresponds to O.0025♂r
1 Vide Tornøe’s Memoir "On the Carbonic Acid in Sea-Water."
2 Zeitschrift für anal. Chemie, 1878, S. 305.
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