HYDROGRAPHY. ^ 



That we better can form an idea of the quantity of oxygen at the single observation of 

 plankton, is, because we have here a fixed normal value for the absorbed quantity, provided that 

 organisms were not existing in the water. A constant generation of oxygen will then at any moment 

 of time have the effect of producing a supersaturation of oxygen, while a constant consumption of 

 oxygen will be the cause of incomplete saturation. If these agencies cease to act, generation of oxygen 

 and consumption of the same, the water will when some time has elapsed— though it be not a very short 

 time — through the effects of the atmosphere, obtain the normal quantity of oxygen which it should 

 have according to the law of absorption. 



With exception of the determinations of sulphuric acid mentioned on page 133, I have not 

 succeeded in finding that the determinations of the quantity of sulphuric acid which is held in the 

 water at different places, is regulated by any special law. It seems to appear from the determinations 

 of sulphuric acid on page 95 — 100 that the ratio between sulphuric acid and chlorine is a quantity that 

 varies so little — even in water with very different qualities — that we cannot by the methods of 

 analysis generally used, obtain determinations of so great exactness that reliable results can be gained 

 in so far as the variations of the aforesaid ratio are concerned. Still it is to be noticed that this is 

 only said in respect of ocean-water. 



Owing to the influence of the glass on the alkalinity, I dare not embark on a discussion 

 regarding the results obtained through the determinations of alkalinity. As, however, there may be a 

 possibility of the determinations being of some consequence, they have been embodied in the table 

 on page 95 — 100. 



PLANKTON. 



In recent hydrographic investigations the plankton-determinations have become a matter of 

 extraordinary importance. In consequence of this a great deal of samples of plankton have been 

 taken on the Ingolf Expedition, but they have not as yet been subject to a final investigation, and I 

 have therefore not been able in the foregoing to have recourse to this important expedient. 



Sent in in the month of January 1898. 



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