450 ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 



The figures quoted below as the results of analyses have been rounded 

 off as whole numbers, since their interest lies in their comparative 

 rather than their absolute value, for convenience they are quoted 

 as " alkalinities," although we are fully conscious that the methods 

 used do not warrant this assumption, and that their actual chemical 

 significance is still obscure. 



The mean value for " outside water " was found to be fairly constant 

 at 40-0 mgrm. OH 7oc> which figure agrees with results obtained by 

 otliers for average ocean water. Samples from the aqnarium tanks 

 never gave as high figures as this, the average being approximately 

 37"5 mgrm. OH 7oo- From this it seems that the amount of base in 

 equilibrium with COg in tank-water is appreciably less than in 

 outside water. A series of thirteen samples taken from seven miles 

 beyond the Eddystone to well inside the Cattewater (an inner tidal 

 harbour near Plymouth) showed a gradual lowering of the alkalinity 

 from the normal 40, to 38 mgrm. OH V^o as the water became more 

 estuarine and polluted. 



The addition of Miquel's sol. B to sea-water was found, on analysis, 

 to reduce the "alkalinity" by an amount equivalent to 10 mgrm. 

 OH 7„o or more. The 1 cc. sol. B added to a litre of sea-water, 

 in itself contains a certain amount of free acid, equivalent to less than 

 4 mgrm. OH 7oo- ^^^^ tliis reduction of alkalinity cannot be accounted 

 for by the addition of free acid alone, because if only a quarter of the 

 amount of sol. 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 sol. B are added as separate solntions, thus obviating any addition 

 of free acid, a reduction equivalent to about 6 mgrm. OH 7oo is still 

 obtained. The presence of ferric chloride in sol. 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 : — 



3 R^COgAq. +Fe2Cl6Aq. - 6 RCl.Aq. + FeoOgAq. + 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 equi- 

 librium with COo, 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 Miquel's sol. B and animal 

 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. 



