520 THE DEPTHS OF THE SEA. [CHAP, x- 



more dilute the solution, the easier would be the decomposition. 

 Adopting Erlenmeyer's view of the position of the halhydration 

 water in sulphate of magnesia (HO Mg S0 2 OH), we 

 might suppose the carbonic acid simply to replace the molecule 



of water, thus Mg < ~ *^ ' ^ ut ^ wou ^ be contrary to 



all analogy for such a body to be more stable in dilute than 

 in moderately concentrated solutions of the same temperature. 

 If, on the other hand, we suppose the C0 2 to interpose itself 

 between the Mg and the basic HO, we have a body of this form : 

 HO CO Mg S0 2 OH. It is conceivable that 

 such a body would in the process of concentration become dehy 



drated, when the anhydrous salt Mg\Q~ C(f/ would be 



formed, which would then split up into C0 2 and MgS0 4 . Assuming 

 now that the body formed has this constitution, it is evident that, 

 for a given mixture of sulphate of magnesia, water and carbonic 

 acid, the amount of the above body formed will be a function 

 of the temperature, the pressure and the duration of their 

 action upon one another. Now, at great depths in the sea, where 

 atmospheric influences are insensible, these conditions are most 

 completely fulfilled. The temperature is low, the pressure high, 

 and the time practically unlimited. Sea-water contains on an 

 average about two grammes of crystallized sulphate of magnesia 

 in the litre; and if the reaction were complete, the two grammes 

 of sulphate of magnesia, or one litre of sea-water, would absorb 

 181/4 cubic centimetres of carbonic acid. Supposing only 

 one-fifth part of the sulphate of magnesia to be thus saturated 

 with carbonic acid, we have provision in one litre of sea- 

 water for the removal of oVer 36 cubic centimetres of car 

 bonic acid. We have thus in the sulphates (for the lime- salt 

 appears to act even more energetically) an agent which in 

 the ocean depths performs one of the two important functions 

 of plants in shallow waters and in the air, namely, the removal 

 of the carbonic acid eliminated by the animals; the task of 

 replenishing the oxygen supply is accomplished by the system 

 of ocean circulation. Moreover, it would be difficult to conceive 



