176 



DEPTHS OF THE OCEAN 



Dissolved 

 solids in 

 sea-water 

 as ions. 



Calcium 

 sulphate. 



Calcium 

 carbonate. 



Dittmar's item CaCO^, which was presumably included in 

 order to express the fact that there is on the whole an excess 

 of bases over acids, is obviously incomplete as it stands. From 

 the most recent measurements we gather that a 3 per cent sodium 

 chloride solution, in equilibrium, as regards CO„-tension, with 

 air (which holds good approximately for sea-water), dissolves at 

 25° C. about 0.07 gr. of calcium carbonate per litre. Hence 

 there cannot be as much as 0.13 gr. per litre in sea- water. The 

 surplus base should rather be regarded as a mixture of calcium 

 and magnesium bicarbonates, existing in equilibrium with a 

 certain amount of free CO^, and of the products of their hydro- 

 lytic dissociation, viz. calcium and magnesium hydroxides. It 

 is the two latter which impart to sea-water its alkaline reaction. 



On considering sea-water in its relation to submarine 

 deposits we note that, of all possible combinations of cation 

 with anion, there are three which are much less soluble than 

 any others, and are therefore closest upon saturation and pre- 

 cipitation : these are calcium sulphate, calcium carbonate, and 

 magnesium carbonate. 



From what is known of the solubility of gypsum in brines, 

 and allowing for the excess of SO^, one would suppose that 

 sea-water is very nearly saturated for this salt, and that addition 

 of, for instance, a sulphate would precipitate it. But gypsum 

 is unknown as a constituent of deep-sea deposits (unless of 

 extraneous origin), so that its solubility-limit is evidently never 

 exceeded under submarine conditions. 



Calcium carbonate, on the other hand, occurs, as already 

 stated, in enormous quantities at the bottom of the sea over 

 wide areas. All the lime in it has been derived, by the aid of 

 organic agencies, from the calcium held in solution by sea-water. 



