72 Hydrogen-ion Concenlralion and Electrical Conductivity 



regions. Thus, McClendon found less than 0.01 mg. of nitrogen per 

 liter as nitrates and nitrites at Tortugas, while Raben (1910) found 

 more than ten times these amounts in the North Sea; and, as shown 

 by McClendon, the tropical ocean, despite its high temperature, can 

 eliminate only a small part of its free CO2 by photosynthesis, due to 

 the scarcity of pelagic plant hfe. 



Krogh (1904) calculated that if the average CO2 tension of the 

 ocean is the same as that of the air (about 0.0003 atmosphere), it 

 must contain 27 times as much C'02 as the air. Thus, if the ocean 

 gave off one-tenth of its CO2 to the air, the carbon-dioxide tension of 

 the sea would sink to 0.0002 atmosphere. He found that the CO2 

 in the air of Disko Island, Greenland, ranged from 0.00025 to 0.007, 

 being high with winds from the north and west and low when the 

 wind blew from the south and east. The turbid sea-water at Disko 

 Island had a CO2 tension of 0.0001 to 0.00035, while the clear water 

 in the same region had a tension of 0.00035 to 0.0006 atmosphere, 

 thus apparently lower than that of the surrounding air. 



Also, according to Krogh, the CO2 tension of the surface water 

 between Cape Farewell, southern Greenland, and the Shetland Islands 

 was distinctly lower than that of the air. 



The average CO2 tension of the air over the ocean seems to be about 

 0.000295, this being the mean of 51 observations made by Thorpe 

 between Brazil and England. In 1917, however, using apparatus 

 given to me by Professor McClendon, I tested the CO2 tension of the 

 air over the Pacific between Samoa and San Francisco, but there was 

 apparently no relation between the local CO2 tension of the air and 

 that of the water under the air, this lack of coordination being due 

 in all probabiUty to the great mobiUty and rapid fluctuation in CO2 

 tension in the air as compared with that of the water. It would 

 apparently be necessary to obtain several thousand determinations 

 of the CO2 tension of air over the ocean, taken at all seasons and in 

 all weathers, to determine its mean CO2 tension with accuracy, but 

 the determinations that have been made indicate that it is not far 

 different from that of the air over the land. My average for 83 

 observations made during eight voyages over the tropical Pacific 

 from 23° north to about 10° south latitude is: Temperature 27°, 

 Ph 8.22, CO2 tension 2.99 ten-thousandths of an atmosphere, and 

 salinity 34.87 (range 33.96 to 35.71). Thus the tropical waters 

 appear to have a CO2 tension about in balance with that of the 

 atmosphere. 



If we consider the subtropical and temperate surface water 400 

 miles and more ofT the CaHfornia coast and extending from 35° to 

 23° north latitude near Honolulu, we find for the average of 46 obser- 

 vations that its temperature appears to be 19.8° C, Pii 8.18, the 

 CO2 tension 2.51 ten-thousandths of an atmosphere, and salinity 



