Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
udfort en Række Forsøg til Bestemmelse af de organiske
Stoffes Mængde, om at meddele mig de fornødne Data.
Ifølge ham ere de organiske Stoftes Mængde kun
underkastet meget smaa Variationer, og affarver 1 Litre
Søvand gjennemsnitlig 3 Mgr. Kamæleon, som under
Forudsætning af Reduction til Oxydulsalt kun kan afgive
henimod 0.8 Mgr. Surstof. hvoraf det lettelig vil kunne indsees.
at den dannede Mængde Kulsyre ikke kan være meget
stor. naar Surstofforbruget selv ved en saa energisk
Oxyda-tion som ved Anvendelse af Kamæleon er saa lidet. Og
hvad der især tyder paa. at den Oxydation. som kan
foregaa ved Vandprøvens Henstand under ordinære
Forholde. fuldstændig maa kunne negligeres, er den
Omstændighed, at Schmelck har fundet Søvandets Evne til
at affarve Kamæleon ligestor, hvadenten Vandprøven
undersøges frisk eller først efter aiirelang Henstand.-
At noget af Kulsyren ved den lange Henstand skulde
være fordampet, er der heller ingen Rimelighed for. naar
man erindrer, at Søvandet er en alkalisk Vædske, som
ikke indeholder det mindste Spor af fri Kulsyre, og som
med saadan Kraft holder paa sin surt bundne Kulsyre, at
den i timevis kan koges i det af Jacobsen angivne
Luft-udkogningsapparat med det Resultat, at kun en meget
liden Brøkdel uddrives. Der er aabenbart større Fare
foldet Modsatte, nemlig at der skulde kimne absorberes noget
af Atmosphærens Kulsyre, men for Undgaaelsen af denne
Feilkilde er der sørget ved omhyggelig Opbevaring paa
velproppede Flasker.
Resultaterne synes heller ikke at tyde paa, at
Henstanden skulde have været til Skade for Vandprøvernes
Brugbarhed, iclet* de alle uden Hensyn til den -meget
forskjellige Varighed af det Tidsrum, hvori de have henstaaet,
vise. nogenlunde det samme Resultat, og jeg tror saaledes
ikke at tage meget Feil. naar jeg anser de af mig udførte
Observationer som i alt Væsentligt ligesaa gode, som om
de havde været udførte ombord paa friskt optagne
Vandprøver.
Hvad angaar de af selve Methoden og
Experimenta-tiouen flydende Observationsfeil, da vil de hyppigt udførte
Controlbestemmelser kunne give de fornødne Bidrag til
Bedømmelsen af deres Størrelse, saaledes er vecl 13
Controlbestemmelser for den neutralt bundne Kulsyres
Vedkommende den gjennemsnitlige halve Differents mellem 2
paa samme Vandprøve udførte Observationer bestemt til
0.11 Mgr. per Litre, (Maximum 0.6). og for den surt
bundne Kulsyres Vedkommende til 0.59 Mgr. per Litre
(Maximum 1.35). Foruden den variable Feil vil der imidlertid
i sidste Tilfælde ogsaa være en constant, idet dçt ikke
lacler sig undgaa, at man ved Arbeide i en kulsyreholdig
Atmosphære vil erholde noget om end meget lidet for hoie
Resultater. Naar Feilene ved Bestemmelsen af den surt
bundne Kulsyre er funden at være størst, da er Grunden
dertil for en stor Del at søge deri. at man ved Retitration
med Natronlud, især naar Rosolsyre anvendes • som Index,
erholder en meget skarp Endereaction, medens dette paa
lang A’ei ikke i samme Grad er Tilfælde, hvor Baryt re-
rne with the necessary data. According to his obserations.
the amount of organic matter varies but very slightly.
1 litre of sea-water discolouring on an average 3’"’"’
permanganate of potash; and this quantity, assuming exti-eme
reduction, cannot give off more than about 0.8m?r of oxygen.
Hence it is obvious that the amount of carbonic acid
cannot be very large, considering the limited consumption of
oxygen even with the use of permanganate of potash. But
that the oxidation which can ordinarily result’ from
allowing the water to stand over may be altogether ignored,
is more particularly indicated by the fact of Schmelck
having found the property in sea-water of discolouring
permanganate of potash to be invariably the same, whether the
samples are freshly drawn or have been preserved for years
together.
Nor is there reason to assume, that any portion of
the carbonic acid .should have escaped by evaporation
during the long interval, if we bear in mind that sea-water is
an alkaline fluid, which does not contain the smallest trace
of free carbonic acid, and which retains that present in
bicarbonates with such vigour, that it may be boiled for
hours together in the apparatus devised by Jacobsen for
boiling out air and not part with more than a mere
fraction. Nay. there is obviously danger of the reverse, viz.
that some of the carbonic acid present in the atmosphere
will be absorbed; but that source of error was effectually
avoided by keeping the water in bottles provided with
tight-fitting glass stoppers.
Judging, too. from the results, which were very nearly
the same for all tli’e samples, irrespective of the difference
in- the length of the period during which they had been
preserved, the interval that had elapsed previous to
examination did not appear to have had any injurious effect on
the water for experimental purposes: and hence I feel .
tolerably convinced that my observations in all essential
particulars are as reliable as if they had been conducted
on board with freshly drawn’water.
With respect to the errors of observation involved in
the method itself, numerous test-determinations will serve
as an approximate standard by which to compute their
magnitude; thus, for instance, half the difference
between-two observations’with the same sample of water was found,
for the carbonic acid forming carbonates, to be.0.1 \""jr per
litre (maximum 0.6), and ’for the carbonic acid forming
bicarbonates to be 0.59m♂r per litre (maximum 1.35). Exclusive
of the variable error there will also, in the latter case, be
a constant one. inasmuch as the results of experiments
perfoj-med in an atmosphere containing carbonic acid must
necessarily be somewhat, if but a very little, too high.
When the error in the determination of the carbonic acid
forming bicarbonates is found to be greatest, the reason
will be chiefly this, that retitration with soda-lye. more
especially if rosolic acid has been selected as the index, gives
rise to a very decided terminal reaction, which does not
result on the baryta water being titrated with oxalic acid: the
reaction is then much less obvious. It must be likewise
<< prev. page << föreg. sida << >> nästa sida >> next page >>
