On Changes in the Sea and Their Relation to Organisms. 257 



tend to show that the particles in the mud are in some way retarded or 

 prevented from getting into equilibrium with the water. 



In order to be sure of clean surfaces of natural calcareous substances, 

 a specimen of coral, Mceandra clivosa, was ground and powdered in a 

 mortar and agitated with sea-water in the same manner as in previous 

 experiments. The results were similar to those with mud (fig. 8). 



There seems to be a more soluble form of calcium carbonate (the 

 juCaC0 3 of Johnston), but since it can not be obtained in a pure state 

 no attempt was made to prepare it. One experiment, however, was 

 made with a precipitate of CaCO 3 that appeared as spherical grains 

 under the microscope. It was agitated for 12 hours with sea- water and 

 the alkaline reserve was 0.0022 at pH 7.95. No further experiments 

 were made to determine whether equilibrium had been approximated. 



These experiments clearly show that the surface water of the sea is 

 a supersaturated solution of CaC0 3 ; and it is only necessary to intro- 

 duce calcite crystals in order to cause considerable precipitation of this 

 substance. Precipitation goes on in the bodies of organisms in the 

 surface waters of all seas. The precipitation observed by Vaughan 

 at Tortugas is very finely divided, but whether it was formed in the 

 bodies of minute organisms, which subsequently died, has not been 

 determined. Such particles might slowly grow, since the agitation of 

 them with sea-water was found to take a trace of CaCOs out of the 

 water. Small crystals have been seen in the bodies of Protista and, 

 whether they are CaC0 3 or not, they might form nuclei for the precipi- 

 tation of CaCO 3 if released into the sea-water. 



TABLE 25. 



In some experiments in liter flasks of resistance glass, filled to the 

 neck (and hence admitting but slight loss of C0 2 ) , the pH and alkaline 

 reserve were determined immediately before and after agitation with 

 calcite. The loss of C02 from the sea-water was estimated in two ways : 



(1) the remaining C0 2 was calculated from the pH and alkaline reserve; 



(2) the loss of CaC0 3 was calculated from change in alkaline reserve. 

 In table 25, the agreement is very striking, in view of the probable 



error in determination of pH and the liability to loss of C0 2 from the 

 water surface in the neck of the flask, agitated by the r otary stirrer. 

 If the pH of sea-water should be maintained (by the action of plants) 



