OCEANOGRAPHY: J. F. McCLENDON 
615 
Not all of the calcium is, however, in the form of CaCOs and Ca"*, 
for some is undissociated CaCU, CaS04, Ca(0H)2, and CaHCOs. The 
chlorides and sulphates are constant but [CaHCOs] and [Ca(0H)2] 
change with the total CO2 content of the sea water. But I have shown" 
that if the alkaline reserve remains constant, the total CO2 of sea water 
(within limits found in nature) varies inversely with the pH ( = — log.H' 
concentration). Hence the. determination of the pH may be substi- 
tuted for that of the total CO2. The determinations I have made of 
the water of the Pacific and North Atlantic showed the pH to vary 
from about 8.1 to 8.25 and those of Dr. A. G. Mayer in the Pacific 
showed only a little wider range (below 8). Earlier observations at 
Tortugas gave the same range, but my more extended observations 
made this summer demonstrate the inadequacy of a few determina- 
tions. The pH is influenced by plant and animal life and rises at 
Tortugas to 8.35 during the day over well-lighted bottoms rich in vege- 
tation, and falls to 8.18 during the night. It may be said, therefore, 
that conditions in shallow water over eel-grass or other sea-weed or 
corals (with symbiotic algae) favor the precipitation of CaCOs-^ 
The question arises whether the occasional high pH of Tortugas sea 
water is sufficient to explain the precipitation of CaCOs, or whether 
nuclei for the separation of the solid phase are necessary. A large 
amount of CaCl2 may be added to sea water without causing a pre- 
cipitation. If the pH is increased by the addition of NaOH, the re- 
sult depends on the speed at which the alkali is added. If the NaOH 
is added suddenly in the form of a strong solution, colloidal precipita- 
tion membranes form about the drops and if the membranes are broken 
by shaking or stirring, a great mass of Mg(0H)2 is included in the pre- 
cipitate. If a very dilute solution of NaOH is added very slowly, CaCOs 
possibly contaminated with Mg(0H)2, is precipitated. The exact pH 
at which precipitation first occurs cannot be determined by this method 
as the first precipitation occurs before the solutions are mixed and the 
crystals thus formed serve as nuclei for further precipitation. If 
Tortugas sea water is kept in glass bottles, precipitation occurs on the 
glass while the pHof the water is within the natural limits, but the pH 
at the glass surface is higher, due to solution of glass. 
Although the pH at which precipitation would occur without nuclei 
for the separation of the solid phase, may be practically impossible to 
determine, the final equilibrium with an abundance of nuclei is not a 
difficult problem. Calcite and aragonite crystals to serve as nuclei were 
produced by the methods of Johnston, Merwin and WilHamson.^ The 
crystals were examined under the microscope and tested with cobalt 
