On the Precipitation of Calcium Carbonate. 19 



apparent dilatation of mercury in this glass is g 3^0 • The correction to be 



,• ^ u ^- r u • • K .u f 1 {V°+T){T-t) 

 applied to the reading of the reverser is given by the lormula , 



where T = the temperature registered by the reverser, t = the temperature 

 shown by the auxiliary thermometer at the moment of reading, and V = 

 the volume (expressed in degrees of the stem) of the secondary bulb and 

 the portion of the stem below the 0° mark of the reverser. 



The thermometers were mounted in pairs in simple metal cases, and 

 were attached just below the water-bottle. They were suspended in a 

 vertical position by a catch forming part of the water-bottle; this was 

 released by the first messenger, when the thermometers fell by their own 

 weight and so reversed, and were hauled up in this position. This simple 

 arrangement proved quite as satisfactory as any of the more complicated 

 reversing frames which are generally In use. 



CULTURE MEDIA AND METHODS. 

 The culture media employed for isolating and counting the bacteria in 

 plate cultures were the following. 



/. Peptone agar: Peptone, 2.0 grams; potassium nitrate (KNO3), 0.5 gram; sea-water, 

 1,000.0 c.c; agar agar, 18.0 grams. 



In the earlier work less agar was used, but eventually it was found more 

 convenient to use a stiflfer jelly, and this did not appear to appreciably 

 hinder the growth of the bacteria. 



II. Potassium malate agar: Potassium malate (C2H3(OH)<^ ^qqj^I, l.o gram; 



sodium phosphate (Na2HP04, 12H2O), 0.25 gram; potassium nitrate (KNO3), 

 0.5 gram; sea- water, i ,000.0 c.c. ; agar agar, 12.0 grams. 



The medium was only filtered through glass-wool, so that a very slight 

 floccular precipitate of calcium phosphate was retained. 



III. Peptone gelatin: Peptone, 2.0 grams; potassium nitrate (KNO3), 0.5 gram; 



sea-water. 1,000.0 c.c; gelatin, 150.0 grams. 



This medium was used only at the Tortugas ; it was necessary to keep it 

 cooled with ice to about 20° C, as the temperature of the laboratory some- 

 times rose as high as 37° C. and gelatin media will not remain solid at these 

 temperatures. 



The following fluid media were used : 



/. Gran's medium {modified): Potassium nitrate (KNO3), 0.5 gram; sodium phosphate 

 (Na2HP04, 12H2O), 0.25 gram; calcium malate (C2H3(OH)<('(-.QQ^Ca^, 

 about 5.0 grams; sea- water, 1,000.0 c.c. 



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

 Gran used distilled water and added 30 gm. sodium chloride per liter, but 

 in these experiments sea-water has been used instead. 



II. Calcium succinate medium: Calcium succinate ^ C2H4<(' ^qq^ Ca 1, 2.0 grams; 



potassium nitrate (KNO3), 0.5 gram; sodium phosphate (Na2HP04, 12H2O), 

 0.25 gram; sea-water, 1,000.0 c.c. 



