THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 497 



After 120 liours a dense cloud, scum, and bulDbles developed in the culture, 

 .and moderate Nitrite and faint Ammonia reactions were given. 



After 131 hours a faint cloud, scum, and bubbles developed in the culture, 

 and very faint Nitrite and faint Ammonia reactions were given. 



After 146 hours a faint cloud and scum, no Nitrite or Nitrate, and very 

 slight Ammonia reactions were given. 



Twenty cultures from samples of water taken well out to sea from 

 Port Koyal were made, and the process of denitrification followed 

 through with each. All gave very similar and consistent results, but 

 the rate of denitrification decreased rapidly with the temperature at 

 which the cultures were grown : thus at an average temperature of 

 27° C. the first trace of the Nitrite reaction appeared after about 

 40 hours, and denitrification was complete after about 100 hours. 



The results of precisely similar experiments that I made with 

 samples of water taken from the English Channel near Plymouth in 

 the autumn of 1909, showed that there the process of denitrification 

 was very much slower, and was never complete at the room tempera- 

 ture (17° C). The first trace of the formation of a Nitrite in cultures 

 in the modified Gran's medium, as detected by the Metaphenylene 

 diamine reaction, occurred about the fifth day, and a large proportion 

 of the Nitrite and Nitrate always remained, even in the oldest cultures. 

 In similar cultures incubated at 30° C. denitrification was complete by 

 the eighth day at earliest, but uniformly consistent results were not 

 obtained, as in some of the cultures complete denitrification never 

 occurred, even after several months. 



It would thus appear that even under similar temperature conditions, 

 the marine bacteria in the seas off Jamaica are much more active in 

 causing denitrification than those found in the English Channel, and 

 since the rate of denitrification is a function of the temperature, it 

 follows all the more that the destruction of Nitrates by bacterial 

 agency in the seas round Jamaica must be far in excess of that 

 occurring in the cooler waters of the English Channel. 



THE INVESTIGATION OF SAMPLES OF SEA-WATEE 

 TAKEN AEOUNI) THE DEY TOETUGAS. 



The Dry Tortugas consist of a group of eight small Keys, the largest 

 of which. Loggerhead Key, is only about ^ mile long by ^ th wide. They 

 are situated about 150 miles from the mainland of Florida, and 

 form the extreme western end of the chain of the Florida Keys. 

 The 100-fathom line lies some 30 miles to the S. and S.W. of the 



