252 Papers from the Department of Marine Biology. 



ON THE CHEMICAL PRECIPITATION OF CaC0 3 IN SEA-WATER.* 



The question of the solubility of calcite and aragonite in sea-water 

 is a matter of interest in relation to the geology of limestone and dolo- 

 mite. Murray and Hjort maintain that sea- water is so complicated 

 a mixture that the solubility of CaC0 3 can not be calculated with cer- 

 tainty (from the law of mass action), but that the experiments of An- 

 derson and of Cohen and Raben show that sea-water is saturated with 

 calcite. They add (p. 181) that dolomite is less soluble than calcite 

 in carbonated water. Their book summarizes observations showing 

 that calcium carbonate is precipitated in shallow tropical waters, but 

 that even shells are dissolved in the red-clay bottoms of the depths. 



Mayer (1916) placed pieces of Cassis shell in sea- water for more than 

 a year and found that they maintained their weight within about 0.1 

 per cent. The precipitation of CaC0 3 at Tortugas was studied by T. 

 Wayland Vaughan, R. B. Dole, and G. H. Drew. Drew observed that 

 a denitrifying bacillus, Pseudomonas calcis, obtained from the sea-water 

 was capable of changing calcium nitrate to calcium carbonate in cul- 

 ture media and supposed a similar process to occur in sea- water. Since 

 Vaughan has observed that calcium carbonate is constantly precipi- 

 tating at Tortugas, Drew's hypothesis necessitates the presence of an 

 appreciable amount of nitrates or nitrites, and I have attempted to 

 determine them. 



A half liter of sea- water was boiled in an all-glass still and the distil- 

 late collected in a series of 25 c.c. Nessler's tubes; another series of 

 Nessler's tubes were filled with a graded series of concentrations of 

 ammonium chloride; 1 c.c. of Nessler's reagent was added to each tube 

 and agitated; after 15 minutes the tubes were compared colorimetri- 

 cally and the ammonia recovered from the sea- water was estimated; 

 after no more ammonia could be distilled from the sea-water, amal- 

 gamated aluminium shavings were introduced into the still and the 

 distillation process was repeated. The ammonia recovered was formed 

 by reduction of nitrates and nitrites. Duplicate analyses gave less 

 than 0.01 mg. of nitrogen per liter as ammonia and less than 0.01 mg. 

 nitrogen per liter as nitrates and nitrites. Raben found more than 

 10 times these quantities in North Sea water (Murray and Hjort, 

 p. 368). Evidently Pseudomonas calcis and other organisms have 

 almost completely removed the fixed nitrogen from Tortugas sea- 

 water. The effect of this probably explains the scarcity of life in 

 the vicinity of Tortugas as compared with colder seas (law of mini- 

 mum). There is, however, a constant renewal of fixed nitrogen from 

 the atmosphere, from the decay of organisms, and probably from water 

 rising from the depths of the ocean. If Pseudomonas calcis is an im- 

 portant agent in the precipitation of CaC0 3 , its action is evidently more 



*The content of this section was published as a separate paper in the Proc. Nat. Acad. Sci., 

 1917.ui, 612. 



