218 



Papers from the Department of Marine Biology. 



METHODS. 



The opportunities offered permitted of continuous observations at 

 two stations, stations A and B, figure 4 (east and west of Logger- 

 head Key, Dry Tortugas), more or less systematized observations 

 around Tortugas (fig. 4), and a series of observations on board between 

 Tortugas and New York City (fig. 3). 



The number of grams of chlorine per kilogram of sea-water (abbrevi- 

 ated CI) was determined by titration with silver-nitrate solution, 

 using potassium chromate as indicator and standardizing the whole 

 method with sea- water standardized by the International Commission. 

 The number of cubic centimeters of 

 O2 per liter was determined by the 

 Winkler method. The self-closing 

 water-bottle was not adequate for 

 this purpose, but some observations 

 were made on water drawn up 

 from about 60 meters through glass 

 and rubber tubing attached to the 

 wire of a Lord Kelvin sounding-ma- 

 chine, and run continuously through 

 the analysis bottle before reaching 

 the pump. Twice the volume of the 

 tube was run through the sample 

 bottle with the least possible suc- 

 tion before the analysis was made. 

 The alkaUne reserve was recorded 

 as the number of cubic centimeters 

 of 0.01 N HCl used in titrating 

 100 c.c. of sea- water while boiling 

 in a 500 c.c. Erlenmeyer ''nonsol" 

 flask, using di-brom-o-cresol-sulfon- 

 phthalein as indicator, until all trace 

 of purple color had disappeared. 

 The end-point is not sharp, but is 

 sharper with this indicator than 

 with any other yet found. The 

 water must not dry on sides of 

 flask. The pH was determined 

 colorimetrically (McClendon, 1917), 

 correction being made for CI. The 

 total CO2 per liter was determined 

 from the alkaline reserve and pH by 

 means of the conversion table. 



Fig. 3. — Oxygen in surface water taken on 

 voyage from Key West to New York. The 

 track of the steamer at night is marked by 

 heavy black Unes. The numbers denote the 

 cubic centimeters of O2 per Uter at the sta. 

 tions marked ^. 



