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36
at fjerne det vedhængende Søsalt. Ganske fuldstændig sker
dette først ved Kogning, men ved Analyserne er forresten
en Behandling med koldt Vand tilstrækkelig, da det kun
er forsvindende Mængder af Salt, som bliver tilbage i Leret.
Bundprøverne tørredes derpaa ved omtrent 100° C.1
Nogle Gram udtoges og glødedes i en Platindigel i Perrot’s
Ovn til konstant Vægt, for at bestemme Vand og organiske
Stoffe (Glødningstab). Af den samme Prøve afveiedes 5
eller 10 Gr. — alt efter Lerets Ensartethed — og kogtes
i en Kolbe med 80 eller 40 Kc. fortyndet Saltsyre (20
pCt.) i omtrent et Kvarter.
Ved nøiagtig at anvende denne samme
Behandlingsmaade ved de forskjellige Analyser faar man nogenlunde
overensstemmende Resultater for den dekomponerbare Del
af Bundprøven, især vecl de finere Slamarter (Biloculinler).
Ved nogle Kontrolanalyser, jeg har udført for at forsikre
mig om Rigtigheden heraf, har jeg ikke faaet nogen større
Variation end 2—3 pCt.
Filtratet fra det saltsure Udtræk fortyndedes til 500
eller 250 Kc. Med en Pipette udtoges af Oplosningen 50
eller 25 Kc., hvori Jern, Lerjord, Kalk og Magnesia
bestemtes ved de sædvanlige Fældningsmidler.
En foregaaende Inddampning for at fjerne den opløste
Kiselsyre blev tildels udført, men er forøvrigt unødvendig,
da denne’Bestanddel af Bundprøven kun forekommer
sporvis i det saltsure Udtræk.
I en anden Portion bestemtes Jernoxydul ved
Titrering med Kamæleon; den saihlede Jernmængde fandtes paa
samme Vis efter Reduktion med Zink.
Det i Saltsyre uopløste Residuum udkogtes med en
Opløsning af kulsurt Natron til Bestemmelsen af Kiselsyren
i de dekomponerede Silicater, blev derpaa glødet til
konstant Vægt i Perrot’s Ovn og veiet. En Del deraf (0.8
til 0.9 Gr.) opsluttedes med kulsurt Kali-Natron,
Kiselsyren fraskiltes, og af Filtratet udfældtes Lerjord -f Jern
og Magnesia paa almindelig Maade. Det første Bundfald
opløstes efter Veiningen i koncentreret Saltsyre2, Jernet
bestemtes derpaa ved Fældning med Ammoniak, efterat
Lerjorden var fjernet med Natronlud.
For med Hurtighed at kunne bestemme Mængden af
1 Hvad enten man anvender 100° eller 110°, gjør ingen
væsentlig Forskjel.
2 Ved denne Behandling kan det være vanskeligt at faa
Bundfaldet fuldstændig opløst, men dette er heller ikke nødvendigt, da det
tilbageblevne uopløste væsentlig bestaar af Lerjord; selv om denne
skulde indeholde smaa Mængder af Jern. er den ialfald ved
Behandlingen med Saltsyre blevet skikket til at paavirkes af Natronlud,
hvorved Jernoxydet bliver uopløst. Dette har jeg ved Forsøg
overbevist mig om.
water, to get rid of the salts. This cannot however be
done entirely without boiling the mass; but for ordinary
chemical analyses, repeated washing in cold water is quite
sufficient, the residue of salt still remaining in the
substance being hardly appreciable.
The portion of deposit was then dried at about 100°
C.1, after which a few grammes, placed in a platina crucible,
were thoroughly heated in one of Perrot’s furnaces, to
determine the proportion of water and organic substances
(loss by ignition). From the same portion, 5 or 10 grammes
— according as the deposit was more or less homogeneous
in character — were next weighed off and boiled in a flask,
for about a quarter of an hour, along with 80cc or 4060 of
diluted hydrochloric acid (20 per cent).
By exclusively adopting this method, fairly congruous
results may be obtained for the decomposable part of the
substance analysed, especially as regards the finer deposits
(Biloculina clay). With divers test-analyses specially made
to substantiate the trustworthiness of the-process in question,
the greatest difference did not exceed 2 or 3 per cent.
After dissolving the sediment filtered from the
decoction with hydrochloric acid, and diluting the fluid till its
volume had reached 500"’ or 250cc, the iron, alumina,
lime, and magnesia in 50cc or 25** of the solution —
drawn off with a pipette — were determined in the usual
manner.
Previous evaporation, to get rid of the silicic acid,
was had recourse to for some of the analyses, though such
is not strictly necessary, traces only of that constituent
occurring in the decoction.
In another portion of the same sample, protoxide of
iron was determined by titrating with permanganate of
potash, and the total. amount of iron in like manner
after desoxidation with zinc.
The residue insoluble in hydrochloric acid was boiled
along with a solution of carbonate of soda, to determine
the proportion of silicic acid present in the decomposed
silicates, and was then thoroughly heated in one of
Perrot’s furnaces, and weighed. Part of it (0.8—0.9 gramme)
was fused with carbonate of potash and soda, the silicic
acid got rid of, and alumina, iron, and magnesia
precipitated in the usual manner. The first deposit was
dissolved, after weighing, in concentrated hydrochloric acid,2
and the iron then present determined by precipitation with
ammonia, the alumina having been previously abstracted by
means of soda-lye.
To determine in a short space of time the proportion
1 Whether at 100°’or 110° makes very little difference.
2 Thus treated, it may be difficult to dissolve the whole of the
deposit: but this is not necessary, the undissolved residue consisting
chiefly of alumina; and even if it should contain minute quantities
of iron, the treatment with hydrochloric acid will have rendered
it susceptible to the action of soda-lye, causing the oxide of iron
to* remain undissolved. Of this I have satisfied myself by direct
experiment.
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