395 



made, but, even if it does, I am of opinion that the effect upon 

 the alkalinity of the sea will remain below our analytical power M. 



Under this heading must also be mentioned the possibility 

 that the assimilation of the plants may sometimes so greatly 

 diminish the tension of carbonic acid in the seawater that a 

 precipitation of carbonates can take place. My experiments 

 show, however, that such precipitation requires so great a 

 diminution of the tension that it is practically impossible, except 

 perhaps in narrow bays where there is an abundant vegetation 

 as in the example mentioned on p. 389. 



b. Decomposition of organic substance. Whereas the 

 formation is practically confined to the upper layers of the sea, 

 where the water is constantly mixed and the physical and 

 chemical conditions are well defined, disintegration may take 

 place everywhere and through the most different intermediate 

 stages. No fixed rule with regard to its influence upon the 

 alkalinity can therefore be given, and observation and experiment 

 must decide everything. 1 think it probable that in stagnant, 

 or, in comparatively stagnant waters, where oxygen is scarce, 

 organic acids and perhaps sulphuretted hydrogen may be formed 

 and the alkalinity thereby appreciably diminished. On the other 

 hand the abundant production of carbonic acid under such 

 circumstances will enhance the solution of carbonates, if such 

 be present ^), and there is also the possibility of a formation 

 of ammonia. 



A fine example of the influence of decaying organic sub- 

 stances in the presence of CaCO^ and MgCO^ is given by 

 Walther & Schirlitz (Zeitschr. Deutch. Geol. Ges., Bd. 38, 1886, 



') At a very moderate estimate an additional alkalinity of O.i (cc. of car- 

 bonic acid) obtained in this way would correspond to a production of 

 0.1 gr. of dry organic substance in 1 1. of water. 



') In Challenger, Narrative vol. 1 p. 917 it is stated that the Blue Mud 

 forming the most extensive deposit around the continents often contains 

 sulphuretted hydrogen while calcareous remains are sometimes quite 

 absent. 



