620 
CHEMISTRY: HENDERSON AND COHN 
present be attached, illustrate the general character of this effect, which 
is dependent mainly upon the first factor mentioned above. 
Temperature Hydrogen ion 
degrees Salinity concentration 
0 32.45 0.141 X 10-7 
10 32.45 0.107 X 10-^ 
20 32.45 0.085 X 10-^ 
30 32.45 0.060 X 10"^ 
40 32.45 0.0446 X 10-^ 
These measurements indicate that under ordinary circumstances, 
when unaffected by the products of metabolism or the constituents of 
river water, the reaction of the sea water is fully determined by (1) 
the tension of carbonic acid, (2) the concentration of water, or salinity, 
and (3) the temperature. This relationship suggests a method of de- 
termining the carbon dioxide tension of sea water, which will be pub- 
lished later. 
4. Hydrogen Ion Concentration of Natural and Artificial Sea Water. — 
So far as the acid-base equilibrium is concerned, sea water may be exactly 
imitated by a system consisting only of water and sodium chloride to- 
gether with carbonic acid, and boric or silicic acid, partly combined with 
alkali. Thus, if a solution be prepared containing 
NaCl 35.0 g. per liter 
NaaCOa 0 . 1035 g. per liter 
H3BO3 0.0620 g. per liter 
Na2B407 0 . 0253 g. per liter 
and set up in series with sea water of salinity 32.45, the two systems, 
after saturation with carbon dioxide at any tension between 0 and 760 
mm., will possess the same hydrogen ion concentration, as estim^ated by 
indicators. This result, however, in that it is comparative, eliminates 
all estimations of the acidity of the solution. And accordingly the most 
trustworthy result of the present investigation is proof of the equiva- 
lence, in respect to hydrogen ion concentration, of sea water with this 
artificial system containing boric acid in a concentration 0.0015 molal, 
carbonic acid in an amount determined by the tension of its gas, and a 
single base in a concentration 0.0022 molal, distributed between boric 
and carbonic acids. 
It is now evident that the ocean, which, because of the presence of 
free carbonic acid, was originally acid, and which has been becoming 
more alkaline from the accumulation of basic material, is at present in an 
epoch where the growing alkalinity is checked by the hufer action of 
acids of approximately the strength of boric acid. These acids are prob- 
