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.
40
■ ponei’G neutrale Carbonater maa blive at tilskrive gradvise
Omsætninger mellem de i Søvandet existerende kulsure
Salte og Magnesiaforbindelserne, og de. af Dr. Jacobsen
hos Søvandet iagttagne Egenskaber maa derfor ogsaa i
mere eller mindre Grad tilligge alle andre magnesiaholdige
Mineralvande, eller naar man lægger Roses ovenciterede
Udtalelser til Grund, alle Saltopløsninger, forsaavidt de
foruden Alkalier og Jordalkalier tillige indeholder
opløselige Salte af nogen af de svagere Baser, som med Kulsyren
danner ubestandige Forbindelser. Denne Omstændighed
vil saaledes uden videre stemple saa godt som alle de til
Bestemmelse af Forholdet mellem den frie og bundne
Kulsyre i Mineralvande -anvendte talrige Methoder som mere
og mindre upaalidelige ligeoverfor magnesiaholdige
Mineralvande, idet man ved dem til Bestemmelse af
neutralbunden Kulsyre enten anvender Residuet fra Inddampning
eller paa anden Maade benytter sig af Kogning, hvor den
efter det forhen udviklede vil være’ utilladelig.
Det vil sluttelig ikke være paa urette Sted kortelig
at berøre de Synsmaader, som fra ældre Tider har været
gjort. gjældende, hvad angaar de i Søvandet indeholdte
Carbonater.
Efter.de Fremgangsmaader, hvorved disse af ældre
Forfattere ere bestemte, kunde de naturligvis kun erholdes
udskilte i Form af kulsur Kalk eller, som af enkelte ogsaa
fundet, lidt kulsur Magnesia, men deraf følger ingenlunde,
at de meel Nødvendighed oprindelig skulde forekommet i
Søvandet • under denne Fonn, ja dette er saa langt fra
sikkert, at jeg meget mere skulde være tilboielig til at tro,
at saa ikke er Tilfælde. Koger man nemlig Søvand i det
af Dr. Jacobsen beskrevne Luftudkogningsapparat, undviger
der, som allerede før bemærket, meget smaa Qvantiteter
Kulsyre, ielet man kan fortsætte Kogningen meel vexlenele
Afkjøling en hel Time uden at faa uddrevet mere end en
Brøkdel af Milligram pr. -Litre: Kogepunctet vil her i
Begyndelsen ligge meget lavt, men stiger, efterhaanden som
den undvigende Luft og den dannede Vanddamp forøger
Trykket, meget hurtigt, saaledes at jeg allerede imeler elen
første Halvdel af Operationen .har observeret en Tempera-,
ratur af 89° C. Naar saaledes de i Søyandet indeholdte
sure Carbonater vise en saa haardnakket Modstand mod
Decomposition, at ele i en hel Time skulde saa goelt som
aldeles uden Virkning kunne udsættes for en Temperatur
af omkring 90" C., da synes mig denne Egenskab -at passe
noget bedre paa surt kulsurt Natron end paa sur kulsur
Kalk, og • det vilde desuden falde vanskeligt at forklare
Søvandets tydelige alkaliske Reaction, medmindre man kunde
antage, at Carbonaterne i det Mindste for en ikke ringe
Del bestod af Alkalisalte.
Meel Hensyn paa Qvantiteten af de i Søvandet
forekommende kulsure Salte, da stemme de derover existerende
Opgaver meget daarligt overens, dte lyde i Regelen paa
Spor undertiden enelog paa Intet, medens der af enkelte
igjen er opført forholdsvis store Mængder. Saaledes finder
decomposing when boiled ’neutral carbonates, arises from
the slow reciprocal action of the carbonates and salts of
magnesia it contains, and the properties observed by Dr.
Jacobsen in sea-water must therefore to a greater or less
extent distinguish all mineral waters containing magnesia
compounds, or. according to Rose, in his statements quoted
above, all solutions of ’salts, provided they contain, exclusive
of sodium, potassium, lime, barium, and strontium, also
soluble salts of some oue of the weaker bases; which
along with carbonic acid form inconstant combinations.
Hence, this circumstance clearly -shows, that of the
numerous methods devised for determining, in mineral waters,
the relative proportion of free carbonic açicl and that
present in carbonates nearly all are. when, magnesia is
present, unreliable, since for the determination of the
carbonic aciel present in carbonates, either the resielue from
evaporation or some other result of boiling is had recourse
to, which has been shown to be inadmissible.
Finally, it will not be out of place to uotice the views
originally entertained with regard to the carbonates present
iu sea-water.
By the process accorcling to which the earlier
chemists determined these compounds, they could öf course
obtain them only in the form of car.bouate of lime. or. as
found by some observers, along with a little carbonate of
magnesia; but from this it does not by any means follow
that they necessarily occur in that form in sea-water: nay.
I am myself inclined to believe that such is not the case.
On boiling sea-water in the apparatus described by Dr.
Jacobsen, very small quantities only of carbonic acid are
found to escape; the fluid may be alternately boiled and
cooled for an hour together without liberating more than
a fraction of a milligramme per litre. The boiling-point
with this method will at first be very low,’ but. ou the
pressure being increased by the escape of the air and the
formation of steam, • rapidly rise; even in the first half of
the operation I have observed a temperature of 89° C.
The vigorous resistance to decomposition thus exhibited by
the bicarbonates in sea-water, which admits of their being
exposed; almost without effect for an hour together to a
temperature of nearly 90° C., would rather seem to
indicate bicarbonate of soda than bicarbonate of lime; and
besides, the decided alkaline reaction of- sea-water would be
difficult to explain unless by assuming the carbonates —
or a considerable portion of them at’ least — to consist of
carbonate of. soda’ and potash.
With regard to the proportion of carbonates present
in sea-water, the results as yet obtained agree but very
indifferently: the majority of observers have detected traces
only or noue whatever, whereas some allege to have found
comparatively large quantities, as will be seen from the
following Table.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
