CHAP, v.] GENERAL CONCLUSIONS. 311 



has been determined, the oxygen and nitrogen have also been 

 collected, and have been preserved until our return home, 

 where they will shortly be analyzed. It would be useless to 

 attempt to discuss the results of the carbonic acid determina- 

 tions at present, and befoi'c these analyses have been made, 

 especially as there is likely to be some relation between the 

 amounts of oxygen and of carbonic acid. Independently, how- 

 ever, of the relations which may subsist between the two bodies, 

 it may be gathered from the inspection of the table (Appendix 

 C) that, taking surface-waters alone, the amount of carbonic 

 acid present is many times greater than would be contained 

 in the same volume of distilled water under the same circum- 

 stances. Sometimes it is more than thirty times as much. 



The amount of carbonic acid contained by surface-waters of 

 the same temperatures increases with the density, and conse- 

 quently is greater in the surface-water of the Atlantic than in 

 that of the Pacific, the two oceans being very markedly dis- 

 tinguished from one another by the different densities of their 

 surface-waters. Thus we have a mean of D'OiGG gramme COg 

 per litre in Atlantic surface-water of temperature between 20° 

 and 25° C. and mean density of 1'02727 ; while in the Pacific 

 the mean is 0*0268 gramme in water of 1*02594 mean density : 

 and the mean amount of carbonic acid in Atlantic water of 

 temperature above 25° C. and mean density 1-02659 is 0*0409; 

 while in the Pacific the corresponding water is of mean density 

 1*02593, and contains 0*0332 gramme CO2 per litre. As a rule, 

 other things being equal, the amount of carbonic acid dimin- 

 ishes as the temperature increases ; thus the mean amount of 

 carbonic acid in waters whose temperature was between 15° 

 and 20° was found to be 0*0446 gramme per litre, the mean 

 density being 1*02642 ; while we have seen that in the Atlan- 

 tic the surface-water of temperature above 25° C. and of mean 

 density 1*02659 contains 0*0409 gramme per litre. Also there 

 is usually more carbonic acid in waters taken from the bottom 



