On Changes in the Sea and Their Relation to Organisms. 255 



tion. If Tortugas sea-water is kept in glass bottles, precipitation 

 occurs on the glass while the pH of 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 Williamson. 

 The crystals were examined under the microscope and tested with 

 cobalt-nitrate solution. These observations, together with the mode 

 of preparation, leave httle doubt that the crystals actually were calcite 

 and aragonite. Under the microscope an occasional calcite crystal 

 could be found among the aragonite crystals, but the number was not 

 sufficient to affect the cobalt-nitrate test. These calcite crystals 

 seemingly grew slightly during the experiments, but apparently no 

 new ones were formed. To determine the equilibria, crystals were 

 mechanically stirred or shaken with sea- water in "nonsol" flasks, 6 to 

 14 hours at 30°; then the pH and alkaline reserve were determined. 



The results of agitating 100 grams of calcite crystals with a Uter of 

 sea-water until equilibrium was approximately reached also appear in 

 figure 7. The alkaline reserve is measured on the ordinate and the 

 pH on the abscissa. This shows that sea-water of the surface of the 

 oceans of the whole world is supersaturated in respect to calcite. We 

 may therefore conclude that suitable nuclei for the precipitation of 

 calcite are absent or deficient in number. The solubility of crystals 

 varies inversely with their size, but after they have attained sufficient 

 size to be readily examined with low powers of the microscope further 

 increase has an unappreciable effect on solubility. But such crystals, 

 if present, would rapidly gravitate to the bottom of the sea ; hence the 

 absence of nuclei for precipitation of calcite is what one might expect. 



Aragonite is said to be about 10 per cent more soluble than calcite, 

 but no difference in the point of equilibrium of the two substances with 

 sea- water was detected in these experiments (fig. 8). This may be 

 explained by the fact that a few calcite crystals were mixed with the 

 aragonite, equilibrium was only approximated, and there were slight 

 errors in the determinations. 



During the rough weather, white calcareous mud is stirred with the 

 sea-water at Key West and to a lesser extent at Tortugas, and it was 

 thought possible that the mud granules might form nuclei for precipi- 

 tation and explain the low alkaline reserve at Tortugas and lower 

 alkaline reserve at Kej^ West. On agitating white calcareous mud, 

 dredged from the bottom, with sea-water, no definite equilibrium was 

 reached, even at the end of 4 days. If the alkaline reserve was first 

 lowered by removal of some CaCOs, it remained lower than if shaken 

 with calcite, and if normal sea-water was used the alkaline reserve 

 remained higher than with calcite. It was thought possible that the 



