.25 



derfor Temperaturen steg over 10U". undveg altsaa altid 

 vel maalelige og ofte endog temmelig betydelige Mængder 

 Kulsyre. 



Ved de paa Pomerøniaexpeditionen i 1871 udførte 

 Luftbestemmelser 1 , hvor den tidligere beskrevne Methode 

 med Grasarternes Udkogning under et ved Yanddamp frem- 

 bragt Vacuum anvendtes, sænkedes imidlertid Temperaturen 

 ikke ubetydeligt. og det viste sig da. at man ved denne 

 Temperatur temmelig ofte kun tik næsten umaalelig sinaa 

 Qvantiteter Kulsyre uddrevet sammen med den øvrige Luft. 

 medens de tidligere Uoverensstemmelser mellom tiere med 

 samme Vandprøve gjentagne Udkogninger ogsaa ber gik igjen. 



Jacobsen fandt sig derfor ved dette mærkelige Phæ- 

 nomen foranlediget til nærmere at andersoge Kulsyrens 

 Absorbtionsforbold ligeoverfor So vand. 



Grjennem de Forsøg. som ban i denne Anledning an- 

 stillede. viste det sig da. at man ad andre Veie kunde 

 paavise aldeles uventet store Qvantiteter Kulsyre i det 

 samme Vand. bvoraf man ved en i flere Timer fortsat Ud- 

 kogning effcer Bunsens Methode kim kunde erholde meget 

 smaa Mængder. Afdestilleredes nemlig Søvandet i en kul- 

 syrefri Luftstrøm " uden Luftfortynding i en Retorte, undveg 

 der den hele Tid Kulsyre. lige indtil den hele Mængde 

 Vædske var afdestilleret, saaledes at man først ved rigelig 

 Udskillelse af Salte kunde være fuldstændig sikker paa at 

 have erholdt det samlede Udbytte af Kulsyre uddrevet. 



Der lod sig under Udkogningen ikke paavise noget 

 Punct, hvor man kunde tale om en Grændse mellem fri 

 og surt bunden Kulsyre. 



Paa denne Maade uddrev nu Jacobsen ved fuldstæn- 

 dig iVfdestillation af 1 j i Litre Søvand i en kulsyrefri Luft- 

 strøm den hele Mængde Kulsyre og opsamlede den efter 

 Pettenkoffers Princip i en afmaalt Mængde titreret Baryt- 

 vand. som efter endt Ojæration retitreredes med Oxalsyre. 

 og beregnedes efter disse den samlede Kulsyremængde. som 

 for ufortyndet Xørdsovand opgives til omkring 100 Mgr. 

 per Litre. 



Samtidig bestemtes ogsaa i Residuet fra Inddampning 

 af circa 10 Litre af det samme Vand den i de neutrale 

 Carbonater indeholdte Kulsyre til i. Middel kun omkring 

 1U Mgr. per Litre. 



Ifølge disse Observationer kunde altsaa kun en meget 

 liden Brøkdel af den ved Destillationen uddrevne Kulsyre 

 betragtes som surt bunden, 'og Jacobsen imødegaar derfor i 

 sin Afhandling bestemt den af Vierthaler- gjorte Antagelse, 

 at al den ved Kogning af Sovandet uddrevne Kulsyre skulde 

 være surt bunden. Han anser sig endvidere aldeles sikker 

 for under Inddampningen ikke at have erholdt decomponeret 

 nogen Del af de i Søvandet indeholdte neutrale Carbonater. 

 idet han udtrykkehg siger: "Die ganze Menge der nicht 



'Ann. Cheni. Pharm. 167 — -1. 



- Wien. Acad. Ber. [2] — 56 — 479. 



Den norske Nordhavsexpedition. Tornøe : Chemi. 



ing-process was conducted with full atmospheric pressure, 

 or at a temperature of more tkan 100° C, invariably proved 

 appreciable, nay sometimes rather large. 



When performing the air-determinations ' on the 'Pom- 

 erahia' Expedition in 1871 (Ijy the metbod, previously 

 described. of boiling out the gaseous elements in a vacuum 

 created by steam), the temperature kept considerably lower, 

 and the quantity of carbonic acid expelled with the other 

 atmospheric elements at a comparatively low temperature 

 was often immeasurably small: moreover. the variable char- 

 acter of the results. alluded to above. on repeating the 

 boHing-process with the same sample of water again as- 

 serted itself. 



Struck by this remarkable phenomenon. Jacobsen 

 determined to investigate anew the absorptive capacity of 

 sea-water in relation to carbonic acid. 



The experiments of that chemist undertaken with the 

 above object in view afforded conclusive proof of the fact. 

 that large quantities of carbonic acid were still present in 

 water from which a very small amount only could be ex- 

 pelled after several hours' protracted boiling by Buuseus 

 metbod. On distilling in a retort sea-water exposed to a 

 current of air free from carbonic acid. hut not raritied. 

 carbonic acid is found to escape so long as any portion 

 of the fluid remains undistilled. an abundance of solid 

 deposit however being the only indication that all or nearly 

 all the carbonic acid present in the water hasbeen driven off. 



During the proness of- boiling no particular moment 

 could be determined marking the escape of the carbonic 

 acid present as gas and of that which has combined with 

 carbonates to form bicarbonates. 



In this manner, by distillation in a current of air 

 free from carbonic acid. Jacobsen succeeded in expelling 

 the whole amount of carbonic acid contained in '/ 4 litre 

 of sea-water. and collected it. by Pettenkoffers metbod. in 

 a given quantity of titrated baiyta water of known strengtb. 

 which. on the operation being terminated. he retitrated 

 with oxalic acid. computing accordingly the total amount of 

 carbonic acid driven off in the process. Undiluted North 

 Sea water contains according to Jacobsens results ahout 

 100"'» r per litre. 



The amount of carbonic acid contained by the neutral 

 carbonates in the residuary deposit from the evaporation 

 of 10 litres of the jsame water, was also calculated. and 

 found to average only about 10 '"' !7r per litre. 



According to these observations. a very small propor- 

 tion only of the carbonic acid driven off by distillation 

 could have been present in bicarbonates: and hence Ja- 

 cobsen emphatically opposes Vierthalers assumption.- that 

 the carbonic acid boiled out of sea-water occurs in that 

 form. Moreover. he feels quite sure that no portion of 

 the neutral cai - bonates in the water examined was de- 

 composed during the process of boiling. -Die ganze Menge." 

 he says. "der nicht mit Basen zu neutralen Salzen verbun- 



1 Ann. Chem. Phai-m. 16", p. 1. 

 - Wien. Acad. Ber. [2 56, p. 479. 



