The Hydrogen-ion Concentration, etc., of Sea-Water. 27 



concentration, and these OH ions combine with the newly formed H 

 ions to form water again. Any change in the H-ion concentration of 

 sea- water due solely to change in temperature {i. e., provided the 

 temperature change is not allowed to cause a loss or gain of CO2) is 

 within the limits of error of our measurements. All measurements 

 were made with the hydrogen electrode, which under proper conditions 

 is affected only by the hydrogen ions. The indicators that were 

 caUbrated are weak acids and hence should be affected by H ions and 

 not by OH ions. The indicators are affected by Na ions to a slight 

 extent, as given in the calibration table. Temperature changes affect 

 these indicators, but the ordinary changes in temperature affect them 

 so slightly that it has not yet been possible to estimate the temperature 

 correction. Furthermore, the temperature coefficient in sea- water and 

 standard borax solution is probably the same. 



The CO2 tension of a solution is the fugacity or escaping tendency of 

 CO2. It is measured by estimating the partial pressure of CO2 in an 

 atmosphere in equilibrium with the solution — i. e., the pressure of CO2 

 required to prevent the escape of CO2 from the solution. The air is 

 not quite in equilibrium with the surface-water of the sea, so that it is 

 not sufficient to determine the CO2 partial pressure in the air unless it 

 is shaken with sea-water. Since the average CO2 in air is 3 parts in 

 10,000, the CO2 pressure is given in parts per 10,000 of a standard 

 atmosphere of 760 mm. Hg. The total CO2 content of sea-water is 

 the total amount of CO2 that may be obtained from it by boiling or 

 evacuating or aeration with indifferent gas after adding an excess of 

 acid to decompose the carbonates. It is not in the form of a gas in 

 sea-water, but exists in several molecular species: CO2, H2CO3, HCO3', 

 CO3", and carbonates and bicarbonates of all of the bases present. 

 The CO2 is estimated as cubic centimeters of the dry gas at 0° and 760 

 mm., and maj'^ be reduced to milligrams by multiplying by 1.965. 



The H* concentration of sea- water is maintained fairly constant by 

 the presence of salts of weak acids called buffers. These are, first CO2 

 and second H3BO3, H3PO4, Si02, and AS2O3, which are not lost by 

 volatilization under conditions in the sea, and are collectively abbrevi- 

 ated to non-volatile buffers. The Ph of sea- water remains constant so 

 long as these buffers (especially CO2) are not increased or diminished 

 in proportion with the bases combined with them. 



RESULTS APPLIED TO OCEANOGRAPHY AND MEASUREMENT OF 

 RESPIRATION-RATE OF MARINE ORGANISMS. 



All of the Ph determinations were made with the hydrogen electrode, 

 but at the same tmie the indicator method was calibrated so that the 

 results may be duplicated by this more convenient method. The 

 indicators used were mostly selected from the list shown in figure 3. 

 It was found that the sulfophthalein series gave the most reliable 



