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25
derfor Temperaturen steg over 100°, undveg altsaa altid
vel maalelige og ofte endog temmelig betydelige Mængder
Kulsyre.
Ved de paa Pomeraniaexpeditionen i 1871 udførte
Luftbestemmelser1. hvor den tidligere beskrevne Methode
med Gasarternes Udkogning under et ved Vanddamp
frembragt Vacuum anvendtes, sænkedes imidlertid Temperaturen
ikke ubetydeligt, og det viste sig da, at man ved denne
Temperatur temmelig ofte kun hk næsten umaalelig smaa
Qvantiteter Kulsyre uddrevet sammen med den øvrige Luft.
medens de tidligere Uoverensstemmelser mellem flere med
samme Vandprøve gjentagne Udkogninger ogsaa her gik igjen.
Jacobsen fandt sig derfor ved dette mærkelige
Phænomen foranlediget til nærmere at andersøge Kulsyrens
Absorbtionsforhold ligeoverfor Søvand.
Gjennem de Forsøg, som han i denne Anledning
anstillede, viste det sig da. at man ad andre Veie kunde
paavise aldeles uventet store Qvantiteter Kulsyre i det
Samme Vand. hvoraf man ved en i flere Timer fortsat
Udkogning efter Bimsens Methode kun kunde erholde meget
smaa Mængder. Afdestilleredes nemlig Søvandet i en
kulsyrefri Luftstrøm’ uden Luftfortynding i en Retorte, undveg
der den hele Tid Kulsyre, lige indtil den hele Mængde
Vædske var afdestilleret, saaledes at man først ved rigelig
Udskillelse af Salte kunde være fuldstændig sikker paa at
have erholdt det samlede Udbytte af Kulsyre uddrevet.
Der lod sig under Udkogningen ikke paavise noget
Punct, hvor man kunde tale om en Grændse mellem fri
og surt bunden Kulsyre.
Paa denne Maade uddrev nu Jacobsen ved
fuldstændig Afdestillation af Litre Søvand i en kulsyrefri
Luftstrøm den hele Mængde Kulsyre og opsamlede den efter
Pettenkoffers Princip i en .afmaalt Mængde titreret
Baryt-vand, som efter endt Operation retitreredes med Oxalsyre,
og beregnedes efter disse den samlede Kulsyremængde, som
for ufortyndet Nordsøvand opgives til omkring 100 Mgr.
per Litre.
Samtidig bestemtes ogsaa i Residuet fra Inddampning
af circa 10 Litre af det samme Vand den i de neutrale
Carbonater indeholdte Kulsyre til i. Middel kun omkring
10 Mgr. per Litre.
Ifølge disse Observationer kunde altsaa kun en meget
liden Brøkdel af den ved Destillationen uddrevne Kulsyre
betragtes som surt bunden, ’og Jacobsen imødegaar derfor i
sin Afhandling bestemt den af Vierthaier2 gjorte Antagelse,
at al den ved Kogning af Søvandet uddrevne Kulsyre skulde
være surt bunden. Han anser sig endvidere aldeles sikker
for under Inddampningen ikke at have erholdt decompöneret
nogen Del af de i Søvandet indeholdte neutrale Carbonater,
idet han udtrykkelig siger: "Die ganze Menge der nicht
1 Ann. Chem. Pharm. 167 —-1.
2 Wien. Acad. Ber. [2] — 56 .— 470.
Den norske Nordhavsexpedition. Tornoe: Chemi.
ing-process was conducted with full atmospheric pressure,
or at a temperature of more than 100° C.. invariably proved
appreciable, nay sometimes rather large.
When performing the air-determinations 1 on the
’Pom-erania’ Expedition in 1871 (by the method, previously
described, of boiling out the gaseous elements in a vacuum
created by steam), the temperature kept considerably lower,
and the quantity of carbonic acid expelled with the other
atmospheric elements at a comparatively low temperature
was often immeasurably small; moreover, the variable
character of the results, alluded to above, on repeating the
boMing-process with the same sample of water again
asserted itself.
Struck by this remarkable phenomenon. Jacobsen
determined to investigate anew the absorptive capacity of
sea-water in relation to carbonic acid.
The experiments of that chemist undertaken with the
above object in view afforded conclusive proof of the fact,
that large quantities of carbonic acid were still present in
water from which a very small amount only could be
expelled after several hours’ protracted boiling by Bunsen’s
method. On distilling in a retort sea-water exposed to a
current of air free from carbonic acid, but not rarified,
carbonic acid is found to escape so long as any portion
of the fluid remains undistilled, an abundance of solid
deposit however being the only indication that all or nearly
all the carbonic acid present in the water has been driven off.
During the process of- boiling no particular moment
could be determined marking the escape of the carbonic
acid present as gas and of that which has combined with
carbonates to form bicarbonates.
In this manner, by distillation in a current of air
free from carbonic acid, Jacobsen succeeded in expelling
the whole amount of carbonic acid contained in litre
of sea-water, and collected it, by Pettenkoffer’s method, in
a given quantity of titrated baryta water of known strength,
which, on the operation being terminated, he retitrated
with oxalic acid, computing accordingly the total amount of
carbonic acid driven off in the process. Undiluted North
Sea water contains according to Jacobsens results about
100 per litre.
The amount of carbonic acid contained by the neutral
carbonates in the residuary deposit from the evaporation
of 10 litres of the [same water, was also calculated, and
found to average only about 10’mgr per litre.
According to these observations, a very small
proportion only of the carbonic acid driven off by distillation
could have been present in bicarbonates: and hence
Jacobsen emphatically opposes Vierthaler’s assumption,2 that
the carbonic acid boiled out of sea-water occurs in that
form. Moreover, he feels quite sure that no portion of
the neutral carbonates in the water examined was
decomposed during the process of boiling. LiDie ganze Menge."
he says, i4der nicht mit Basen zu neutralen Salzen verbun-
1 Ann. Chem. Pharm. 167, p. 1.
2 Wien. Acad. Ber. [2] 56," p. 479.
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