AGENCIES IN DEPOSITION OF CALCIUM CARBONATE 739 



solubility, since the diminution of the solubility-product constant 

 of calcite with temperature is, as we have seen, proportionally less 

 than that of the absorption coefficient of C0 2 . 



The abstraction of C0 2 from a saturated solution results ulti- 

 mately, then, in the deposition of CaC0 3 , no matter what the agency 

 which abstracts the C0 2 . This agency may be a diminished pro- 

 portion of C0 2 in the air, or a higher temperature, or both; or it may 

 be organisms which make use of the C0 2 in their vital processes, or 

 the production by bacterial action of ammonia, which indirectly 

 achieves the same result; or, in short, it may be any way in which 

 the concentration of C0 2 may possibly be diminished. Conse- 

 quently, if the surface layers of the sea are saturated, as we believe 

 they are, precipitation of CaC0 3 will be brought about wherever 

 any of the foregoing agencies are operative. 



In this connection two points which are the consequence of 

 accepting erroneous chemical data are to be noted. Thus Davis 1 in 

 his excellent work on marls has made a slight slip. He observed that 

 on bubbling oxygen gas through a solution containing CaC0 3 the 

 latter was precipitated, and he attributed this effect to a specific 

 action of the oxygen; but any other gas would have produced the 

 same effect, which was actually due to the sweeping out of the C0 2 

 from the solution. Nor is it necessary to consider, when ammonia is 

 being produced, whether it appears as hydroxide or as carbonate, or 

 whether there is a subsequent metathesis with calcium sulphate or 

 chloride or some other reaction; in either case the net result can be 

 predicted immediately from a consideration of the effect of the added 

 substance upon the concentration of calcium-ion and of carbonate- 

 ion, 2 and of the magnitude of the product [Ca ++ ] [CO 7] in relation 

 to its precipitation value. 3 To some this procedure may appear 

 complicated; in reality, while it pays no heed to those easily derived 

 arithmetical equations so often considered as representing reactions, 

 it takes into account the several equilibria which must be adjusted, 



1 C. A. Davis, Jour. Geol., VIII (1900), 487. 



2 Change of concentration of CO 7 affects, and is affected by, the concentration of 

 HC07 and OH - , these being all dependent variables; see Johnston, op. cit. 



J Provided that calcite is still the stable solid phase in equilibrium with the solu- 

 tion; cf. footnote 3, p. 733. 



