KELLERMAN AND SMITH! CALCIUM CARBONATE 401 



2. Calcium carbonate may be precipitated from water laden 

 with calcimn bicarbonate by bacterial production of ammonia 

 according to the formula: 



Ca(HC03)2 + 2NH4OH = CaC03 + (NH4)2C03 + AO 



3. Calcium carbonate may be precipitated as a result of the 

 bacterial decomposition of calcium salts of organic acids such as 

 calcium succinate, calcium acetate, or calcium malate. The 

 denitrification of nitrates also takes place in these cultures and 

 perhaps is essential to the formation of calcium carbonate. The 

 formulae for this reaction have not yet been determined. 



From our experimental work it seems probable that the precip- 

 itation of calcium carbonate described by Drew as occurring in 

 solutions supplied with organic compounds of calcium is due to 

 the calcium liberated from the decomposing molecule of the 

 organic calcium salt. We have produced rather large crystals of 

 calcium carbonate by the growth of certain bacteria in media 

 which contained no calcium whatever except in the form of organic 

 salts. In this connection it should be noted that denitrification 

 of nitrate will not in all cases produce the ammonia necessary for 

 some of the reactions referred to above. Where a culture medium 

 remains alkaline during the production of nitrite further produc- 

 tion and accumulation of ammonia is possible. Where the culture 

 medium is faintly acid, however, in the first stage of the fermen- 

 tation, the nitrite is produced, and with the production of even 

 minute traces of ammonia a decomposition of the resulting am- 

 monium nitrite takes place with the liberation of free nitrogen, 

 according to the formula: j 



NH4NO2 = N2 + 2H2O 



A study of Drew's original description of Bacterium calcis, as 

 well as careful study and staining of similar organisms isolated 

 from samples of water collected near the Florida Keys, shows 

 beyond doubt that the proper genus for this organism is Pseudo- 

 monas. New data for identification are given in the following 

 description : 



