THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 505 



the products of decomposing vegetable matter, provided that the 

 Nitrate supply, and conditions of light and temperature, were suitable. 

 Such conditions should be especially well fulfilled by the drainage into 

 the sea of a well- wooded country with a calcareous subsoil, and the 

 soluble organic calcium salts would be precipitated as Calcium car- 

 bonate by the action of the bacteria. In addition, the elimination of 

 the acid radical from the Xitrate in the process of denitrification, by 

 whatever stages it may occur, must leave the alkaline base free to destroy 

 the normal equilibrium of the salts in sea-water, and by increasing 

 the alkalinity, would also result in the precipitation of Calcium car- 

 bonate. 



To test this theory cultures were made in a medium having the 

 following composition : — 



Calcium succinate . . . 2*5 grammes 

 Potassium nitrate . . . 0"5 „ 

 Sea-water .... 1000-0 c.c. 



Calcium suceiuate is soluble in these proportions, and the medium is 

 quite clear. Free growth was manifested by the cloudiness of the 

 ruedium 48 hours after inoculation, and Xitrite formation was apparent. 



After 96 hours the medium appeared quite milky, and this milki- 

 uess was due to the presence of exceedingly fine particles of a sub- 

 stance which was soluble in dilute Hydrochloric Acid with evolution 

 of gas, and was presumably Calcium carbonate. In some cultures 

 these particles settled as a definite sediment, but in others the 

 particles were so minute that they showed little tendency to settle, 

 and could only be separated by centrifugalization. The condi- 

 tions determining the size of the particles formed could not be 

 ascertained, as the size varied in cultures which were apparently made 

 and grown under identical conditions. 



The addition to cultures in which the particles of Calcium car- 

 bonate were so small as to remain in suspension of any foreign 

 substance, such as finely powdered Calcium sulphate, or of larger 

 particles of sand, resulted in the aggregation around them of the 

 particles of Calcium carbonate, forming a concretion around a central 

 nucleus. These concretions were hard and of almost crystalline 

 appearance under the microscope, and were soluble in dilute Hydro- 

 chloric Acid with evolution of bubbles of a gas which, when the 

 operation was performed on a microscopic slide, could be completely 

 absorbed by running in a solution of Sodium hydrate under the 

 cover-slip. Once this process of concretion had been initiated, it 



