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



29 



be good for 5 years, provided they are kept in the dark most of the 

 time.^ 



Details of the indicator method and the colorimeter that we used 

 are given on pages 44-46, and we will now pass on to the question of 

 the duplication of our results by the indicator method. 



We found the P„ of sea-water to be practically independent of 

 salinity or temperature between 20° and 30°, and all of our experiments 



6 7 8 9 1 

 XlO-w 



xlO-'- 



5 6 7 8 9 1 X10-* 



Hydrogen ion concentration 



5 6 7 8 9 10 



Fig. 4. — Results of electrometric titration of COa-free sea-water plus indicator with COa-free 

 NaOH solution. A verj' slight excess of KCl is added to the water and the CO2 driven off by- 

 boiling, the water is brought about to the neutral point (Ph =7), and then titrated. On the 

 ordinate is measured the logarithm of the number of cubic centimeters of 0.1 normal NaOH 

 added to 100 c.c. of the neutral, COo-free sea-water, and on the abscissa is measured the Pg. 

 At the bottom is a scale for conversion of the Ph into normality of H-ion concentration. 

 The titrations were made on sea-water from the following sources: A, artificial sea-water 

 containing 0.0015 molecular boric acid. B, sea-water from Tortugas, Florida, C, artificial 

 sea-water containing O.OOOS molecular boric acid. D, Tortugas sea-water in which diatoms 

 and other Protista had been grown in a pyrex flask for about 6 months. E, sea-water collected 

 somewhere off Hatteras and kept in the Princeton marine aquarium about 6 years, the evapor- 

 ation being compensated by addition of rain-water. F, artificial sea-water without any non- 

 volatile buffer. Later experiments showed these data to be merely relative. 



at 10° indicate that even this drop in temperature does not appreciably 

 affect the Pg. Our values given for 0° are extrapolated from CO2 data 

 on the assumption that the Ph is independent of the temperature. 



We found the Ph of sea-water to be determined solely by ratio of 

 the concentration of buffers, including CO2 and other weak acids, to 

 the concentration of bases combined with them (excess base over 

 strong acid). 



'Duplicates of our tubes and colorimeter may be obtained from the manufacturers of the 

 indicators. 



