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CHEMISTRY: HENDERSON AND COHN 
THE EQUILIBRIUM BETWEEN ACIDS AND BASES IN 
SEA WATER 
By Lawrence J. Henderson and Edwin J. Cohn 
WOLCOTT GIBBS MEMORIAL LABORATORY, HARVARD UNIVERSITY 
Received by the Academy, October 4. I9I6 
The alkaline reaction of sea water and the chemical equilibria that 
define it concern not only the oceanographer but also the geologist and 
the biologist. For information upon this subject must lead to further 
knowledge regarding geographical variations in the composition of the 
sea, the chemical reactions which have taken place during the existence 
of the ocean, the present movements of carbonic acid upon the earth, 
and the environmental relations of sea water to marine flora and fauna. 
In the present investigation it has been sought, first, to determine the 
influence of carbon dioxide tension and of salinity upon the hydrogen 
ion concentration of sea water and, secondly, to construct a solution 
of exactly known composition, which shall reproduce the behavior of 
sea water when subjected to changes in carbonic acid concentration. 
This task has been accomplished with such accuracy as existing methods 
of investigation afford. The results define the acid-base relation between 
marine organisms and their environment, the fluctuations in this rela- 
tionship, and the means by which such fluctuations are controlled. 
They also yield evidence concerning the geological history of the ocean. 
When combined with the observations of Palitzsch, they lead to 
a general description of the geographical variation in the chemical 
equilibria of sea water and to information concerning the gradients 
along which carbon dioxide is at present moving in the sea and in the 
air. 
1. Hydrogen Ion Concentration and Carton Dioxide Tension of Sea 
Water. — large number of estimations of the hydrogen ion concentration 
of sea water, when saturated with carbon dioxide at tensions between 
0 and 760 mm., have been made. The hydrogen ion concentrations 
were determined colorimetrically, following exactly the procedure of 
Palitzsch, 1 and at first with his kind assistance,^ so that the results are 
strictly comparable with his. The standard solutions were in all cases 
analyzed with the hydrogen electrode. Carbon dioxide tensions, after 
equilibrium had been established, were determined either by chemical 
analysis of the gas phase or with the manometer. The following 
table corresponds to the curve which best fits the data of these experi- 
ments. 
