56 
Forat undgaa de her omtalte Feil, beuyttedes til Be- 
stemmelse af Saltmængden i Sovandet følgende Fremgangs- 
maade. 
I en med tætsluttende Laag forsynet tyk, veiet Por- 
cellaiudigel indveiedés 30 til 40 Gr. Sovand. som afdunste- 
des paa Vandbad. Efterat Saltene fare nogenlunde vel 
tørrede, ophededes Digelen med JLaaget paa ca. 5 Minutter 
over eu Bunsens Lampe, afkjøledes og veiedes paauy. Der- 
efter bestemtes paa den forud beskrevne Maade den ved 
Decomposition af Chlormagnesium dannede frie Magnesia, 
hvorved de til Beregning af den samlede Saltgehalt for- 
nødne Data erholdtes. 
T en tidligere Afhandling 1 har jeg paavist, at Car- 
bonaterne i Sovandet ved Kogning omsætter sig til kulsur 
Magnesia, som ved Inddampning eller under enhver Om- 
stamdighed ved Glødning efterlader Magnesia, og man 
skulde altsaa strengt taget for den saaledes dannede Del 
af den frie Magnesia beregne en anden Correction end for 
den ved Decomposition af Chlormagnesium dannede Hoved- 
mængde. Den Feil, man begaar, ved at undlade dette er 
imidlertid baade meget nær constant og desuden saa liden, 
at den uden videre kan negligeres, idet den kun bidrager 
til at formindske den samlede Saltgehalt med omkring 
0.0015 °/o. Det er saaledes fuldstændig tilstrækkeligt til 
den ved Vein ingen fundne Mængde tørret Salt at' addere 
1.375* Gange den ved Titreringen bestemte Mængde fri 
Magnesia, lor af det saaledes fremkomne Tal at beregne 
Saltgehalten i Procenter. 
Mod denne Methode kan der dog reises Indvendinger. 
idet det kunde befrygtes, at mindre QVantiteter ( 'lilorna- 
trium, Chlormagnesium eller Chlorkalium under Glodningen 
kunde forflygtiges, eller at en Del a f den svov-Isure Mag- 
nesia ved den hoie Temperatur kunde decoiuponeres og 
give Anledning til Tab af Svovlsyre. Man kan imidlertid 
let forvisse sig om, at dette ved Anvendelse af en tyk Porcel- 
laindigel med tætsluttende Laag ikke bevirker nogen Feil 
af mærkbar Indflydelse. Saaledes fandt jeg, at 1.2 Gr. af 
en passende Blanding af Chlorkalium og Chlornatrium ved 
D/i Times starkest mulig Glødning over en Bunsens Lampe 
i den samme Digel, som jeg benyttede til mine Saltbestem- 
melser, kun tabte 2 Mgr. i Vægt. det vil sige, Blandingen 
tabte ved Glodningen ikke fuldt 0.14 Mgr. pr. 5 Minutter. 
Ligeledes paavistes ved Bestemmelse af Svovlsyre og Mag- 
nesia saavel i det benyttede Sovand som i det glodede 
Residuum, at man selv ved en meget længere fortsat Glod- 
ning end . den. der udfordres forat skatte fuldstændig vand- 
frit Salt. ikke risikerer nogen skadelig Feil foranlediget 
ved Forflygtigelse af Chlormagnesium eller Decomposition 
af svovlsur Magnesia. 
* •‘Om Kulsyren i Søvatjilet" Side 40 øverst. 
In order to guard against the above-mentioned errors, 
the following mode of operation was adopted for determin- 
ing the amount of salt in sea-water. 
From 30'"' to 4lC r of sea-water were introduced into 
a thick porcelain crucible of known weight, furnished with 
a tight-fittting cover, and evaporated on a water-bath. So 
soon as the salt was sufficiently dry, the crucible, with the 
cover on. was heated for about 5 minutes over one of 
Bunsen’s gas-burners, then cooled and weighed with its 
contents. The free magnesia liberated by the decomposi- 
tion of the chloride of magnesium was now determined in 
the manner previously described, and the last factor neces- 
sary for computing the total amount of salt accordingly 
found. 
In a former paper 1 I drew attention to the fact, that 
the carbonates present in sea-water are transformed during 
the process of boiling into carbonate of magnesia, which 
after evaporation, or. at least, on the salt being thoroughly 
heated, leaves a residue of magnesia; and hence the pro- 
portion of free magnesia thus formed would, strictly speak- 
ing. seem to involve the need of a correction different from 
that adopted for the principal amount liberated by the 
decomposition of the chloride of magnesium. But the error * 
which arises from applying the same correction to both is. 
on the one hand, very nearly constant, and. on the other, 
so small as to admit of being safely ignored, seeing that 
it reduces the total amount of salt only abtiut 0.0015 per 
cent. It is. therefore, amply sufficient, if to the amount of 
dried salt found by weighing he added 1.375 times the 
amount of the free magnesia determined by titration : the 
figure thus obtained will ser.ve to compute the percentage 
of salt. 
This method certainly is so far open to objection, 
that small quantities of cldoride of sodium, chloride of 
magnesium, or chloride of potassium may be volatilized 
during the - process of heating, or some portion of the sul- 
phate of magnesia be decomposed at the high temperature, 
and thus occasion a loss of sulphuric acid. The error, 
however, arising from this source will not exert any ap- 
preciable influence on the result, provided the crucible 
used for the operation be of thick porcelain, and have a 
tight-fitting cover. Thus, for instance. I found that 1.2-' ,r 
of a proportionate hnixture of chloride of potassium and 
chloride of sodium, on being heated for the space of an 
hour and a quarter over one of Bunsen's gas-burners in 
the crucible I had used for my salt-determinations, lost 
only in weight, or 0.14 m * r every 5 minutes. More- 
over, it was manifest on determining the sulphuric acid 
and magnesia both in the water itself and in the heated 
residue, that» even in the event of the heating-process being 
much more protracted than • is necessary to obtain salt free 
liom the smallest trace of water, no serious error can 
result from the volatilization oi chloride of magnesium or 
the decomposition of sulphate of magnesia. 
s “On the.Cnrbonic Acid in Sea- Water,” p. 40. 
