220 



Papers from the Department of Marine Biology. 



10,000. A new aneroid barometer was used and the mean value for 

 2 months was taken as 760. A thermometer graduated down to tenths 

 of a degree was standardized by the United States Bureau of Standards 

 and the other thermometers compared with it. A recording ther- 

 mometer for the air w^as compared with the mercury thermometer, but 

 the records were not found to be of much value in relation to the sea. 

 Tortugas is about on the heat equator during July. There was a 

 diurnal variation of the temperature of the air from 25° at dawn to 

 30° at 1 p. m., with a very slight upward drift during July and with 

 a few variations due to storms. All time records are in local apparent 

 time. The weights used were standardized by the United States 

 Bureau of Standards and the glass apparatus and solutions stand- 

 ardized by weighing. 



All water samples that could not be examined immediately were 

 preserved in large flasks of resistance glass entirely full of the sample 

 and were examined as soon as possible. Most of the samples taken at 

 night were titrated by artificial light. The pH was in such cases deter- 

 mined with the aid of a ''daylite" lamp, but the results were not very 

 satisfactory'. 



Samples (for pH) taken a short time before sunrise were kept in 

 nonsol flasks for the pH to be determined after sunrise. 



The CO2 tension at 30° was found from the pH, using table 2. The 

 correction for other temperatures was made possible by the fact that 

 a change of 1° temperature corresponds to 0.01 pH. The unit of CO2 

 tension is one ten-thousandth of a normal atmosphere (760 mm. Hg) 

 of CO2. 



Table 2. 



The sea-water was usually supersaturated or undersaturated with 

 oxygen. The number of cubic centimeters of O2 per liter at saturation 

 at a given temperature was read from figure 5 and the excess or defi- 

 ciency of saturation of the water was recorded. Figure 5 com- 

 pares favorably with the results of Fox, who used a different method 

 of analysis. Jacobsen's formula for cubic centimeters O2 per liter 

 at saturation is 10.062-0.2822 t- 0.006144 t" -0.000061 t^ -0.1073 

 CH-0.003586 tCl-0.000055 t^Cl. t=temperature and Cl=grams 

 chlorine per kilogram of sea-water. 



