622 



wells: solubility of calcite in water 



as it flows southward. Taking the analyses used by Palmer/ 

 we have the following data on this point: 



Bicarbonate content of Mississippi Rive)' water at various localities 



The figures in the last column above are not exactly compar- 

 able with the solubilities in pure water recorded in this paper on 

 account of the presence of other salts, a varying acidity and a 

 varying calcium ion concentration, but they are believed to illus- 

 trate the dependence of the solubility of calcium carbonate on 

 the temperature. 



Another application of the varying solubility may be found 

 in the formation of marble from coral. Certain islands in the 

 Philippines, having shores of coral, are found to consist, at fairly 

 shallow depths, of limestone. It may be that the compara- 

 tively rapid conversion of coral into limestone is due to the fact 

 that with every fluctuation of temperature, many particles of 

 calcium carbonate alternately dissolve in, and re-deposit from, 

 small amounts of water in the pore space, tending always toward 

 the more stable calcite. 



In making analyses of natural waters the temperature at the 

 time of collection should be noted, for, although calcium car- 

 bonate may not actually deposit before the analysis can be made, 

 owing to the slowness of the change illustrated by Table II, the 

 question of whether the water was saturated or not when col- 

 lected would require for its satisfactory answer a knowledge of 

 its temperature. 



• U. S. Geological Survey Bull. 479, p. 28. 



