734 JOHN JOHNSTON AND E. D. WILLIAMSON 



untrustworthy. 1 On the other hand, the concentration of free CO., 

 in any water, at a given temperature, can be calculated by means 

 of the known absorption coefficient of C0 2 , if the proportion of CO, 

 in the atmosphere with which it has been in contact is known; 2 and 

 as at the present time this proportion is usually close to 3 parts in 

 10,000 the corresponding solubility of calcite in natural waters 

 should be close to the values given in Table II. Consideration of 

 the published analyses 3 from this standpoint leads to the conclusion 

 that the surface layers of the warmer portions of the sea (in so far 

 as they have been investigated), as well as many river waters, 4 are 

 substantially saturated with calcite. Murray, 5 in adverting to this 

 question, states the opinion that " the ocean as a whole remains just 

 about saturated for calcium carbonate"; but this statement is 

 without doubt too sweeping, except in the sense that the concentra- 

 tion of CaC0 3 throughout the ocean is probably as great as it is in the 

 warm surface layers. But there is also more direct evidence. Thoulet 6 



1 The titration methods which have usually been employed for the determina- 

 tion of free C0 2 — and to some extent of combined C0 2 — are altogether untrustworthy, 

 since the results depend upon the amount of indicator added and upon other factors 

 which have not been adequately controlled. This question is discussed at length in 

 another paper (J. Johnston, Jour. Am. Chem. Soc, XXXVIII [1916], 947). Cf. also 

 Morgulis and Fuller, Jour. Biol. Chem. XXIV (1916), 31. 



3 With regard to the solubility of C0 2 in a sea-water see C. J. J. Fox, Trans. 

 Faraday Soc, V (1909), 68. 



s See F. W. Clarke, Data of Geochemistry; but especially a paper by E. Dubois, 

 "The Amount of the Circulation of CaC0 3 and the Age of the Earth." (Proc. 

 Acad. Wetenschappen Amsterdam [1901], PP- 43-62). Cohen and Raken (ibid. 

 [1901], p. 63) have determined directly the solubility of CaC0 3 in an artifical sea- 

 water at 1 5 and found about 55 parts per million; but their method of experiment 

 is not unexceptionable and would tend to yield low results; they also conclude that 

 this sea-water is saturated with CaC0 3 . Wells also (Jour. Wash. Acad. Sci., V 

 [1915], 621) points out that the amount of carbonate carried by the Mississippi 

 River diminishes steadily as it flows southward, i.e., in the direction of rising 

 temperature. 



4 Indeed, the amount carried by many rivers is much in excess of the true solu- 

 bility, indicating that some of it is in suspension. Where such a river reaches the sea, 

 the salts cause the flocculation of this and any other suspended material, and in this 

 way induce the formation of deposits there. 



s Murray and Hiort, The Depths of the Ocean (191 2), p. 180. 

 6 J. Thoulet, "Etude bathylithologique des cotes du Golfe de Lyons," Annates 

 de ITnstitut Oceanographique, IV, fasc. VII (1912), pp. 32-35. 



