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



39 



For plants at least it is permissible to add a drop of the strong solution 

 per liter and allow it to precipitate. If cultures are grown in soft 

 glass, no further additions of Si will be necessary to supply that used up 

 by diatoms. 



When sea-water is evaporated and redissolved oxides of manganese 

 and iron, CaS0 4 , Si0 2 , Ca 3 (P0 4 ) 2 , CaC0 3 , CaF 2 , Ca(B0 2 ) 2 , A1 2 3 , 

 Ba(B0 2 ) 2 , BaS0 4 , and, under certain conditions, MgNH 4 P0 4 are diffi- 

 cult to get into solution, but by adding HC1 and evaporating, a paste 

 containing gypsum will be obtained which will go into solution in 

 about 3 days and may be neu- 

 tralized and 0.21 gram NaHCO 3 

 per liter added. 



Another method of determin- 

 ing the C0 2 tension on board 

 ship or in laboratories without 

 general chemical equipment was 

 developed. The portable micro- 

 apparatus for determining the 

 total CO 2 , described in section 

 4, was used and conversion 

 tables were prepared for deter- 

 mining the C0 2 tension from 

 the total C0 2 , the temperature, 

 and the excess base. Figures 

 7, 8, and 9 are conversion tables 

 for finding the CO 2 tension of 



Sea-Water of 23, 24, and 25 excess FlG - 7. Conversion table for finding the CO 2 ten- 

 . . i -n i Slon of sea-water of 23 excess base from the 



base, respectively. Each curve 



is for the indicated temperature 



only, and the values for 



were extrapolated. Tables for 



sea-water of any other excess base titration may be plotted with the 



aid of figure 10, which shows the change of CO 2 with change in excess 



base when other factors are constant. 



Although it is theoretically a simple matter to determine the C0 2 

 tension directly, in practice it has been most difficult and attended with 

 large experimental errors. Perhaps the most direct method is to shake 

 a large quantity of the sea-water with a small quantity of air in a bottle 

 until equilibrium is established, and analyze the air in the bottle. 

 Errors arise in failure to reach equilibrium or to correctly determine 

 the pressure and temperature or to correctly analyze the air. The 

 analysis of one part of C0 2 in 10,000 parts of air may be done by the 

 titration method, in which there are solubility and other errors, or 

 by measuring the gas-volume contraction after absorption of C0 2 , 

 in which there are temperature, pressure, and meniscus errors. A 



38 



2 4 5 6 7 8 9 10 



CO, pressure in 0.0001 atmo^ohere 



temperature and total CC>2. Each curve is for 

 only one temperature, and that for has been 

 extrapolated. On the ordinate is given the 

 total CO2 and on the abscissa the COa tension 

 in ten-thousandths of an atmosphere. 



