Carbon-Dioxide Content of Sea-Water at Tortugas. 93 



15 to 20 minutes. This method gives sharp results, but the alka- 

 Hnity thus found probably includes a small amount due to substances 

 other than carbonates. 



For the alkalinity due to carbonates alone the method at present 

 used by the writer is as follows: A slight excess of 0.02 normal sul- 

 phuric acid is added from a burette to 100 c. c. of sea-water in a non- 

 sol flask. The mixture is then boiled 15 to 20 minutes, while a gentle 

 stream of pure air is passed into it to assist in blowing out the carbon 

 dioxide. (This step might be done under reduced pressure.) The 

 solution is then titrated back with 0.02 normal sodium hydroxide, 

 using cresol red (o-cresolsulphonephthalein) as indicator. This indi- 

 cator is not entirely satisfactory, but is used in order to arrive at an 

 end point of approximately the same Ph value as sea-water. If 

 this end point is not used the titration will include in part the acidifi- 

 cation of certain substances besides carbonates that are present in 

 sea-water. The water is first more than acidified in order to assure 

 the removal of all carbon dioxide. 



The record of determinations made at Tortugas is given in table 1 . 

 Figure 1 shows the relation between the carbon-dioxide content of 

 the water and time of day. 



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DiTTMAR, W. 1884. Challenger Rept., Physics and Chemistry, vol. 1, p. 215. 



Fox, C. J. J. 1909. Faraday Soc. Trans., voL 5, p. 82. 



McClendon, J. F. 1918. Carnegie Inst. Wash. Pub. No. 252, pp. 213-258. 



Mayor, A. G. 1919. Proc. Amer. Philos. Soc, vol. 58, p. 150. 



Murray and Hjort. 1912. The depths of the ocean. 



ScHLOsiNG, T. 1880. Compt. rend. 90, p. 1410. 



Wells, R. C. 1918. U. S. Geol. Surv. Prof. Paper 120-A. 



WooD-JoNES, F. 1910. Coral and atolls. 



