THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 491 



III. Peptone Gelatin. 



Peptone 2*0 grammes 



Potassium nitrate (KNO3) ..... 0*5 „ 



Sea- water 1000-0 c.c. 



Gelatin 150*0 grammes 



This medium was only used at the Tortugas. It was necessary to 

 keep it cooled with ice to about 20° C, as the temperature of the 

 Laboratory sometimes rose as high as 37° C, or even higher, and 

 Gelatin media will not remain solid at these temperatures. 



The following fluid media were used : — 



I. Gran's Medium (Modified). 



Potassium nitrate (KNO3) . . . . . 0'5 gramme 

 Sodium phosphate (Na^HPO^, 12HoO) . . . 0-25 



Calcium malate (€2113(011) <pQQ>Ca), about . S'O ,, 



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



Calcium malate is only slightly soluble in water, so can be added in 

 excess. Gran used distilled water, and added 30 grammes of Sodium 

 chloride per litre, but in these experiments sea-water has been used 

 instead. 



II. Calcium Succinate Medium. 



Calcium succinate (C2H^</-iQQ>Ca) . . . 2*0 grammes 



Potassium nitrate (KNO3) ..... 0*5 „ 



Sodium phosphate (NaoHPO^, 12HoO) . . 0*25 

 Sea- water ........ lOOO'O c.c. 



This medium was boiled and filtered before sterilization, to remove 

 the slight precipitate of Calcium phosphate. It was found that this 

 medium with the addition of the phosphate gave a more vigorous 

 growth than if it was omitted. 



III. Calcium Acetate Medium. 



Calcium acetate (Ca(CH3COO)2) .... 5*0 grammes 

 Sodium phosphate (Na._>HP04,i2H20) . . 0*25 



Potassium nitrate (KNO3) . . . . . 0'5 „ 



Sea-water ........ lOOO'O c.c. 



Boiled and filtered before sterilization to remove precipitate of 

 phosphate. 



