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overdragne, til Undersøgelser over Saltgehalten udelukkende
anvendt Egenvægtsbesteninielser. hvorimod jeg paa de to
sidste Togter vecl Siden af disse ogsaa har udført et større
Antal Chlortitreringer for gjennem denne Control at give.
Resultaterne en større Sikkerhed.
Til Undersøgelser over den i Søvandet indeholdte
Chlormængde medhavdes .paa de to sidste Togter foruden
Sølvopløsning af saadan Styrke, at 1 CC. af denne omtrent
svarede til 1 CC. Søvand, ogsaa 2 paa første Togt
indsamlede Vandprøver, bestemte til som Normaler at tjene
til den nøjagtigere Fastsættelse af Sølvopløsningens Styrke.
Disse Normalers Chlormængde i Procenter blev ved
omhyggeligt udførte Veiningsanalyser hvert Aar bestemt saavel
før Expeditionen Udreise som efter dens Hjemkomst
bestandig med meget nær det samme Resultat, hvorhos tillige
deres Egenvægter ved Hjælp af Aræometret ombord
aflæstes. Til Brug ved alle ombord udførte Chlortitreringer
tjente kun to Btiretter af lignende Construction og
Størrelse. de samme, som af Stipendiat A. Helland anvendtes
ved de Bestemmelser af Chlormængderne i Overfladevandet
i Atlanterhavet, som denne foretog i Aaret 1875 paa en
Reise til Grønland, de bleve af ham den Gang calibrçrede
ved Hjælp af Kviksølv og befundne særdeles tjenlige for
Øiemedet.
Ved Buretternes Brug fyldtes den ene med
Sølvopløsning den anden med det til Undersøgelse bestemte
Søvand. hvorefter en passende Portion Søvand fra den ene
under Omrystning tilsattes Sølvopløsning fra den anden,
indtil al Chlor var udfældt. idet chromsurt Kali tjente som
Index.. Begge Buretters Stand aflæstes nu, og nogle
Draaber Søvand tilsattes atter til Affarvning, hvorefter paany
fulgte Tilsætning af Sølvopløsning og Aflæsning af
Biiret-t£rnes Stand o. s. v. gjennem en Række af 4 a 5 paa
bilsiden følgende lignende Aflæsninger erholdtes paa denne
Maade de fornødne Data til Beregning af det Volum
Søvand. som i hvert enkelt Tilfælde svarede til 1 CC.
Sølvopløsning.
Paa denne Maade sammenlignedes paa den ene Sicle
Søvandsprøverne og paa den anden Side ogsaa fra Tid til •
anden de medbragte Normaler med Sølvopløsningen, idet
der altid sørgedes for. at Vandprøvernes og Opløsningernes
Temperatur ikke fjernede sig synderlig meget fra hinanden.
Biiretterne bleve for at tilveiebringe en bedst mulig
Afløb-ni ng hyppig rensede med concentreret Svovlsyre.
Af de gjennem disse Observationer erholdte Tal er
senere Søvandets Chlormængde beregnet efter følgende
Formel
K S P
}) = HcT
hvori p betegner den undersøgte Vandprøves Chlormængde
i Procenter, k det Antal CC. af samme, der svare til 1
CC. Sølvopløsning og sidens Egenvægt ved 17."5 O.. P
Middeltallet mellem de før Udreisen og efter Hjemkomsten
i Normalen fundne Chlorraængder, K det Antal CC., som
af denne svarer til 1 • CC. Sølvopløsning og S dens Egen-.
work, made exclusive use of specific gravity determinations:
but for a considerable number of my own observations, on
the last two cruises. I also adopted titration for chlorine
as a means of testing the general accuracy of the results.
For estimating the amount of chlorine in sea-water.
I took with me, on the two last cruises, besides a solution
of silver of such strength that 100 of the. fluid about
corresponded to lcc of sea-water, also 2 samples of water
collected on the first voyage, to serve as a normal standard
by which to determine the Strength of the solution of
silver. Each year, both previous to the departure of the
Expedition and after its return, the chlorine in these
standard samples was carefully determined by weighing, and
the percentage calculated accordingly, their specific gravity
too. as shown by the areometer on board, having been
likewise noted down. For all chlorine-titrations performed at
sea. there were only two burettes in use, similar alike in size
and construction. — those used by Mr. Helland for
determining the amount of chlorine in the surface-water of the
Atlantic on a voyage to Greenland in 1875; lie had
calibrated them by means of mercury, and they proved
excellently adapted for the purpose.
When using the burettes, one was filled with solution
of silver and the other with the sea-water selected for
examination, after which solution o"f silver was added to a
proper quantity of the sea-water, while shaking the flask
in which the titration was performed till all chlorine had
been precipitated, chromate of potassium serving as the
index. The height of the fluid in both burettes was now
read, and a few drops of sea-water added to the
mixture, to discolour it, after which solution of silver was again
added, and the height of the fluids read as before, &c.
After the height had been thus read 4 or 5 times in
succession, the necessary data were obtained for computing
the volume of sea-water, which in each individual case
corresponded to 1cc solution of silver.
In this manner, were compared on the one hand the
freshly drawn samples of sea-water, and on the other, from
time to time, also the standard samples, with the solution,
of silver, care being taken to keep the samples of water
and the solution as near as possible at the same
temperature. In order to prevent any portion of the fluid from
adhering to the burettes, they were. frequently rinsed with
concentrated sulphuric acid.
With the figures obtained from these observations, the
amount of chlorine in sea-water was afterwards determined
by the following formula —
KSP ’ -
in which p signifies the percentage of chlorine in the
sample of water examined, k the proportion in cubic
centimetres representing 1cc of the solution of silver, and
s the specific gravity of the water at 17 ° 5 C.; P the mean
between the amounts of chlorine found in the standard
sample before the departure and after the return of the
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