58 



Papers from the Department of Marine Biology. 



40° (which is the highest necessary in biological work) is 338.15, and 

 we have rounded off this value of 338 for all temperatures between 0° 

 and 40°. 



After adding the correction from the above table, the millivolt 

 reading was converted into Ph by the conversion table in figure 20, 

 which was cut into five sections to save space. The larger numbers 

 (1-10) denote P„, the numbers 338 to 950 denote 

 millivolts, and the vertical lines temperatures, as 

 indicated below. The double horizontal scale 

 above is for converting the fractional part of the 

 Ph into the coefhcient used in expressing the 

 hydrogen-ion concentration, tenths of a P„ being 

 denoted by the arrows above, and the coefficient by 

 the finely divided scale below. 



The table at 10°, near bottom of page 57, serves 

 to extend the range, and the table at 30°, just below, 

 serves as a guide to figure 20. 



In choosing the size of the apparatus for the 

 analysis of the total CO2 in the sea-water, it was 

 necessary to consider the fact that we had to 



Fig. 21. — Van Slyke plasma CO2 apparatus as used for the deter- 

 mination of the total CO2, Oj, and N2 of sea-water. The absorp- 

 tion pipette P may he omitted and a simple stopcock used on the 

 top. A piece of small-bored suction rubber tubing, 80 cm. long, 

 is attached to the lower end of the apparatus, and connected to 

 a levcling-bulb with cylindrical sides that is hold up by means of 

 a swivel attachment to a screw passed through a nut held in a 

 burette clamp attached to a tall rod support for the whole ap- 

 paratus. The essential feature of the apparatus is the gradua- 

 tion of the gas burette B in hundredths of a culjic centimeter, so 

 that the gas-volume can be accurately determined with the ap- 

 paratus in the upright position and an upturned water meniscus 

 below the gas. The graduations should go at least half-way 

 around the gas burette to avoid parallax errors. It should be pos- 

 sible to estimate thousandths of a cubic centimeter by means of 

 a lens. 



bring the water sample to a known CO2 tension before the analysis. 

 We foiuid it impossible to make more than a liter of the gas mixture 

 correctly. We made gasometers on a larger scale, but they were 

 unsatisfactory. It was also impossible to bring a large sample of sea- 

 water to a known COo tension with only 1 liter of gas mixture. We 

 finally chose the micro-apparatus used by Van Slyke in determining 

 the total CO2 in blood-plasma. The large compartment of our appa- 

 ratus held 50 C.C., but we would recommend its increase to 100 c.c. 

 The form we used in the first part of the work was essentially like 

 figure 21, but later we cut off the absorption pipette P, and absorbed 

 the CO2 by running NaOH solution directly into the gas burette B. 



