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HYDROGRAPHY. 



A systematic examination of the quantity of carbonic acid contained in sea-water, and 

 the absorbed amount of oxygen and nitrogen, was commenced during the Pommerania Expedi- 

 tion in 1872. Jacobscn boiled out the water-samples on board and analysed the collected gases when the 

 expedition had come home. Through these analyses, he came to the conclusion that the absorbed quan- 

 tity of air is not dependent on the pressure to which the water containing the gases is subject in the sea. 



In the same manner as Jacobscn, Dittmar and Buchanan, after the Challenger Expedition, as 

 well as Tornoe, after the Norwegian North- Ocean-Expedition , made their analyses of the gases con- 

 tained in sea-water. Dr. H.. Tornoc maintained that the temperature of absorption of the water at the 

 time when last it left the surface, could be ascertained by means of the quantity of nitrogen it con- 

 tained. By the quantity of oxygen that is required to enable the ratio between oxygen and nitrogen 

 to have the same value as it assumes by saturation with atmospheric air, we should be able to estimate 

 the extent of the reducing effect the water has been subject to since the absorption. 



Since the Norwegian North-Ocean-Expedition many analyses have been made of the gases contained 

 in the sea-water, and specially by Professor O. Pettersson , who introduced a new method of working 

 by depositing the water samples in glass-balloons void of air, the boiling and the analysis being 

 effected after the expedition had arrived home. By this proceeding the boiling can be made with 

 far greater care than by Jacobsen's method, but the greatest advantage by Pettersson' s method is, 



