Kalk 1 . Dette Bundfald viste sig at beståa af Magnesia 

 foruden en Smule Jern og Fosforsyre og neppe mærkelige 

 Spor af Kulsyre. Inddamper man derimod en Liter Sø- 

 vand til dens halve Volum, saa danner der sig et Bundfald, 

 som bestaar af kulsur Kalk og Gibs og kun indeholder 

 smaa Mængder Magnesia. Men hvorvidt den kulsure Kalk, 

 som i dette Tilfælde udskiller sig. virkelig fra Begyndelsen 

 af har været opløst som saadan i Sovandet. kan naturligvis 

 ikke afgjøres ved dette Forsøg. Tvertimod synes det med 

 megen Rimelighed at fremgaa af Hr. Tornoes Undersøgel- 

 ser over Kulsyren i Søvandet, at denne fortrinsvis maa 

 være bundet til Natron som dobbelt kulsurt Salt. 



Ved videre Iriddampning af Sovandet udskilles Gips 

 og, Klornatrium. Endnu etterat Hovedmassen af Kogsaltet 

 bar afsat sig. indeholder Moderluden alle de Kali- og Mag- 

 nesiåsalte, der fra Begyndelsen af har været tilstede i 

 Våndet. I en saadan Moderlud fra 20 Liter Søvand- ryk- 

 kedes det mig at paavise .Jod efter den af Koetstorier- 

 angivne Methode. Ved Afkjoling under 0° udskilte den 

 Krystaller af svovlsurt Natron, ved høiere Temperatur 

 svovlsur Magnesia. 



Forchhammer angiver i sin Afhaudling om Søvandet, 

 at ban flere Gange bar fundet Svovlvandstof i de hjem- 

 sendte Prøver. Han tilføier imidlertid, at denne Forbin- 

 delse muligens kan være opstaaet ved en mindre omhygge- 

 lig Rensning af Flaskeme ; men i enkelte Tilfælde foler 

 ban sig dog forvisset om, at den maa have dannet sig af 

 Søvandets egne Bestanddele. Jeg har aldrig kunnet op- 

 dage den karakteristiske Lugt af denne Gas ved Aabningen 

 af de fra Expeditionen medbragte Vandprøver. Selv nogle 

 af disse, der undtagelsesvis vare blevne opbevarede i almin- 

 delige, med Korkpropper forsynede, Flasker og først aab- 

 nedes efter et Par Aars Forløb. befandtes at være fuld- 

 kommen lugtfrie. 



Efter Forchhammer's Mening skulde Svovl vandstoffet 

 have dannet sig ved Oxydation af de organiske Stoffe paa de 

 svovlsure Saltes Bekostning. Foråt bestemme Søvandets 

 organiske Bestanddele benyttede Forchhammer Kogning med 

 Kamæleon, og indførte derved en Methode. der som be- 

 kjendt senere har faaet en udstrakt Anvendelse med Hen- 

 syn til Drikkevand. 



Han tilsatte Søvandet saameget af en bekjendt Op- 

 løsning af overmangansur Kali, at det efter et Opkog og 

 Henstand i 12 Timer beholdt en rødlig Farve. Den i 

 < hcrskud tilsatte Kamæleon fandtes ved at bestemme den 

 Mængde af denne, der var nødvendig foråt frembringe 

 samme Farve i det samme Volumen rent Vand, Ved at 

 anvende denne Methode har jeg fundet, at LOOKc. Søvand 

 ialmindelighed affarver 0.0005 < rr. overmangansur Kali. 

 h vad der omtrent skulde svare til 0.0025 pCt. organiske 



1 Sammenlign Tornøe's Afhandling om Kulsyren i Søva i 

 -' Zeitschrifl fur anal. Chemie, L878, S. 305. 



failed however to detect the slightest trace of lime. 1 The 

 said deposit was found to consist of magnesia, along with a 

 little iron and pliosphoric acid, and hardly appreciable traces 

 of carbonic acid. If. on the other hand. a litre of sea- 

 water be reduced by boiling to half its volume. the precip- 

 itate will consist of carbonate of lime and gypsum, the 

 proportion of magnesia being comparatively small. But 

 whether the carbonate of lime precipitated in this case was 

 originally present as such in the water, is a question which 

 cannot be decided by this experiment. Judging. however. 

 from the results of Mr. Tornøe's observations on the car- 

 bonic acid present in sea-water, that gas may with good 

 reason be inferred to occur chiefly in combination with 

 soda as a bicarbonate. 



On further evaporation of the sea-water. gypsum and 

 chloride of sodium are deposited ; and even after the bulk 

 of the chloride of sodium has been precipitated, the mpther- 

 liquor contains all the salts of potash and magnesia 

 originally present in the water. In mother-liquor of 

 this description, obtained from 20 litres of sea-water. I 

 suCceeded in detecting iodine. by the process described 

 by Koetstorfer. 2 On reducing the temperature. sul- 

 phate of soda was deposited ; on raising it. sulphate of 

 magnesia. 



In the treatise on ocean-water, Forchhammer records 

 his having frequently met with hydrosulphuric acid in the 

 samples of sea-water sent him; and this compound may. he 

 thinks, in most cases, be traeed to impurities in the bottles; 

 though in some he feels convinced it had formed from the 

 constituent parts of the sea-water itself. I did not how- 

 ever in any case detect the fætid smell characteristic of 

 that gas. when opening the numerous phials brougbt home 

 with the Expedition. Oertain of the samples even excep- 

 tionally preserved in common corked bottles, and allowed 

 to stand over for the space of two years, proved to be 

 quite inodorous. 



According to Forchhammer, hydrosulphuric acid is 

 formed by the oxidation of organic matter, at the cost of 

 the sulphates. In order to determine the organic elements 

 of sea-water, Forchhammer boiled the latter with perman- 

 ganate of potash. thus devising a process which has since 

 been extensively adopted for the determination of organic 

 matter in drinking-water. 



He added to the sea-water a solution «ff permangan- 

 ate of potash, of known strength. sufficient to give it. on 

 being boiled and suffered to stand over for the space of 

 12 hums. a reddish colour. The excess of permanganate 

 of potash was found by determining the proportion of that 

 substance necessary to produce the same colour in an equal 

 volume of pure water. Adopting this method, I found 

 that 100 M generallv sufficed to discolour 0.0005*'' of per- 

 manganate of potash, which nearly cprresponds to 0.0025 ?r 



1 Vidi Tornøe's Memoir "On the Carbonic Acid in Sea-Water." 

 Zeitschrifl fur anal. Chemie, i v 7s. S. 305. 



