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 — 0 — SO, — OH), we 
might suppose the carbonic acid simply to replace the molecule 
of water, thus—Mg¢e ag? 9 but it would 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 CO, to interpose itself 
between the Mg and the basic HO, we have a body of this form ; 
HO— CO — 0—Mg— O—SO,— OH. It is conceivable that 
such a body wonld in the process of concentration become dehy- 
drated, when the anhydrous salt Mg Ca O would be 
formed, which would then split up intoCO, and MgSO,. 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- 
bonie 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 
