ARTIFICIAL CULTUllE OF MARINE. PLANKTOJsT ORGANISMS. 399 



But this reduction of alkalinity cannot be accounted for by 

 the addition of free acid alone, because if only one quarter the 

 amount of solution B is added, the alkalinity of the sample 

 will be found to be, if anything*, only very slightly higher. 

 Also, if the various constituents of solution B are added as 

 separate solutions, tlius obviating any addition of free acid, a 

 reduction equivalent to about 6 mgrm. OH °/oo '-^ ^^^^^ obtained. 

 The presence of ferric chloride in solution B gives a possible 

 explanation of this phenomenon. If a solution of ferric chloride 

 is added to a solution of a soluble carbonate, a reaction, 

 which can be expressed by the following equation, takes place: 



SR.CO^Aq. + Fe.ClcAq. = 6 ECl.Aq. + FeAAq. + 3 CO,. 



When the ferric chloride is added to sea-water, the final 

 result will be that a certain amount of the " excess base," 

 which was in equilibrium with CO^, will then be in equilibrium 

 with the chlorine, available on the precipitation of hydrated 

 ferric oxide, with a consequent liberation of COo, and a 

 reduction in "alkalinity " will, therefore, take place. 



An analogy between the actions of MiqueFs solution B and 

 :inimal charcoal can be seen in the fact that water treated 

 with animal charcoal also shows a reduced " alkalinity,^' the 

 amount being very variable in different samples. 



Sea- water treated with HoO^ also showed a lowering of the 

 alkalinity, but in a much less degree when, as usual, minimal 

 quantities were used. 



Control experiments on double distilled water, which had 

 been treated with these substances, were tried, but great 

 difficulty was found in obtaining an end point with the 

 indicator. As far as could be judged, distilled water treated 

 with solution B (quantities as with sea-water) showed a 

 negative " alkalinity," equivalent to about 8 mgrm. OH°/qq, 

 and in the case of animal charcoal a positive alkalinity 

 equivalent to 6 mgrm. OH°/qq, but the colour change was so 

 slow that these results are only the roughest estimates. The 

 possibility that the above results are due to some effect on 

 the indicator, which entirely cloaks the true alkalinity, must 

 always be taken into consideration. 



