39 
Apparat i omkring 2 Timer, idet den undvigende Kulsyre 
som før opfangedes og besteintes ved titreret Jiarytvand. 
I den anvendte Mængdfe Sodaopløsning var iudeholdt G3.3 
Mgr. Soda svarende til 20. 3 Mgr. Kulsyre, medens der 
ved to Experimenter paa denne Maade fandtes uddrevet 
den ene Gang 26.8 og den anden 27.7 Mgr. Ved Kor- 
søgets Gjentagelse med en lidt større Qvantitet paariy ind- 
veiet Soda fandtes uddrevet 34.1 Mgr. Kulsyre istedetfor 
beregnet 33.2. Under Kogningen var Oplosningen i Be- 
gyndelsén fuldstændig klar. hvorpaa der efter circa l /o Ti- 
mes Forløb begyndte at fremkomme et Bundtald a f Mag- 
nesia. hvori der trods al anvendt Moie ikke lykkedes mig 
at paavise det minffste Spor af Kulsyre. Den basisk kul- 
sure Magnesia er nemlig ifølge H. Rose og Flere ikke 
ubetydelig opløselig saavel i Vand som i forskjellige Salte, 
saaledes at der af smaa Mamgder intet Bundtald fremkom- 
mer, og det er derfor ikke paafaldende. at Oxydet ved saa 
fortyndede Opløsninger; som her ere anvendte, ikke udfældes, 
førend det ved Kogningen er befriét for sin Kulsyre. 
lvoges Søvn nd under Concentration, kan man meget 
let komme til at overse denne Udski Helse af Magnesia, 
idet denne først indtræder efter nogen Tids Forlob. saa- 
ledes at man kan antage Blnkningen fremkommen ved Ud- 
fældning afGjps i den concentreredé Vædske. Udskillelsen 
vil ogsaa, naar Inddampningen foregå ar i aabent Kar. for- 
sinkes betydeligt, idet Kulsyrens Undvigen foregaar meget 
langsommere i en kulsyreholdig Atmosphære end i en kul- 
syrefri Luftstrøm, og det kan derfor ikke forundre, at 
denne Udfældning af Magnesia .af kogende Søvand, saavidt 
mig bekjendt. ikke tidligere er observer et, naar undtages, at 
Usiglio 1 i det tørrede Residum hai* paavist fri Magnesia. 
Dersom man imidlertid koger Søvand uden Concentration 
i en kulsyrefri Atmosphære med omvendt Kjøler, saaledes 
som det let kan ske ved Classens Apparat, fremtræder 
Phænomenet meget tydeligt paa samme Maade som ved 
Kogning af en Blanding af Soda og Bittersalt, idet der 
efter circa */s Times Kogning begynder at udskille sig et 
Bundfald bestaaende af ren kulsyre- og kalkfri Magnesia 
ved Siden af et lidet Spor af Kiselsyre hidrørende fra det 
benyttede Glaskar. Om man samtidig opfanger og bestem- 
mer den undvigende Kulsyre, viser det sig, at den Yillig- 
.lied. hvormed Kulsyrén undviger, ikke saameget afhænger 
af Concentrationsgradeu som af Varigheden at det Tids- 
rum, hvori Kogningen fortsadtes, da ogsaa paa denne Maade 
circa 2 Timers Kogning strækker til for at skaffe en tuld- 
stændig kulsyrefri Vædske. 
Det vil forhaabentlig hermed kunne ansees luldstæn- 
dig godtgjort, at Søvandets Evne til ved Kogning at decom- 
. ■ 
Jouru. flir pract. Clicm. 40 — 100. 
paratus for 2 hours exposed to a current' of air free from 
carbonic acid, the carbonic acid driven off being collected 
and determined as before by titrated baryta water. The 
portion of the solution of ' carbonate of soda employed 
contained 03.3 m, J f of that substance, representing 26.3 ms,r 
carbonic acid; and two experiments performed by this 
method gave respectively 26.8 ,n;; ’ and 27.7 as the amount 
of .the latter driven off. On repeating the experiment 
with a somewhat larger quantity of carbonate of soda, 
carefully weighed, 34.1'"0 r were found to have been liber- 
ated. whereas the exact proportion would have been 33.2'"<' r . 
During the process of boiling, the fluid at first continued 
perflectly clear: but after the lapse of about half an hour 
magnesia began to be precipitated, in which with the 
most delicate tests I failed to detect the smallest .trace 
of carbonic acid. According to H. Rose and other authors 
basic carbonate of magnesia is to a considerable extent 
soluble alike in water and in solutions of divers salts, 
so that small quantities give no precipitate and hence 
it is not surprising that with a solution so diluted as that 
made use of for these experiments, the oxide should not 
have been precipitated before it had given off all its car- 
bonic acid. 
If sea-water he boiled during concentration, this 
precipitation of magnesia may be easily overlooked, since 
it does not take place till after the lapse of some time, 
and the turbidness of the concentrated fluid might there- 
fore be ascribed to the deposit of gypsum. When the 
water, too, is evaporated in an open dish, the precipitation 
will be considerably retarded, since the carbonic acid es- 
capes much more slowly in an atmosphere containing car- 
bonic acid than in a current of air from which all car- 
bonic acid has been expelled : and this accounts for the 
precipitation of magnesia in boiled sea-water, so far as 
I am aware, not having been previously observed, except 
at least by Usiglio, 1 who detected the presence of free 
magnesia in the dried residue. When: however, sea-water 
is boiled without being concentrated in an atmosphere 
free from carbonic acid, and with the cooler inverted, which 
it easily may be with Classen’s apparatus, the phenomenon 
appears with great distinctness, as is tin* case on boiling 
a mixture of soda and Epsom salts; for after about half 
an hour's boiling a precipitate begins to form, consisting 
of pure magnesia, with no admixture of lime and carbonic 
acid and a trace only of silicic acid, the latter arising 
from the glass vessel employed in the operation. If the 
carbonic acid be simultaneously collected and determined, 
the readiness with which it escapes is found to depend 
not so much on the degree of concentration as on the 
duration of the boiling-process, about 2 hours proving 
amply sufficient to obtain a fluid tree from the smallest 
trace of carbonic acid. 
From what has been stated, there is. we think, con- 
clusive proof, that the property possessed by sea-water of 
1 Journ. fur pract Chein. 40, p. 100. 
