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, CaS04, SiOa, Ca3(P04)2, CaCOg, CaFz, Ca(B02)2, AI2O3, 

 Ba(B02)2, BaS04, and, under certain conditions, MgNH4P04 are diffi- 

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

 containing gypsum will be obtained which will go into solution in 

 about 3 daj^s and may be neu- 

 tralized and 0.21 gram NaHCOs 

 per liter added. 



Another method of determin- 

 ing the CO2 tension on board 

 ship or in laboratories without 

 general chemical equipment was 

 developed. The portable micro- 

 apparatus for determining the 

 total CO2, described in section 

 4, was used and conversion • 

 tables were prepared for deter- 

 mining the CO2 tension from 

 the total CO2, the temperature, 

 and the excess base. Figures 

 7, 8, and 9 are conversion tables 

 for finding the CO2 tension of 



sea-water of 23, 24, and 25 excess ^^^- 7.— Conversion table for finding the CO2 ten- 



1 i- 1 -ri 1 ^^•^'^ of sea-water of 23 excess base from the 



base, respectively. Each curve temperature and total CO2. Each curve is for 



is for the indicated temperature °^^y ^'^^ temperature, and that for 0° has been 



1 J xu 1 r no extrapolated. On the ordinate is given the 



only, and the values lor U total CO2 and on the abscissa the CO2 tension 



were extrapolated. Tables for ^^ ten-thousandths of an atmosphere. 



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

 aid of figure 10, which shows the change of CO2 with change in excess 

 base when other factors are constant. 



Although it is theoretically a simple matter to determine the CO2 

 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 estabhshed, and analyze the air in the bottle. 

 Errors arise in failure to reach equiUbrium or to correctly determine 

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

 analysis of one part of CO2 in 10,000 parts of air may be done by the 

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

 by measuring the gas-volume contraction after absorption of CO2, 

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



3 4 5 6 



CO picsiiure in 0.0001 atmo?'-.hcre 



7 8 9 10 



