64 



Papers from the Department of Marine Biology. 



results. We could not use it in these experiments on account of the 

 large sample required. 



The oxygen in the sea-water may be determined on the same 

 sample after the CC>2, by absorbing it with an alkaline solution of pyro- 

 gallol, introduced in the same manner as the NaOH solution, and the 

 nitrogen + other inert gases may be determined by the residue. The 

 whole calculation must be repeated for these gases, using their respec- 

 tive absorption coefficients, as given in the following table, calculated 

 from Fox's data, for sea-water of Cl = 20. Fox does not state whether 

 this is Cl per liter or per kilogram. 



One of the most important requirements in such investigations as 

 are described in this paper is accurate temperature control. All of the 

 determinations in Minneapolis were made in a laboratory that was 

 converted into a constant-temperature room by cutting off the steam 

 heat and regulating the temperature by means of a nichrome wire 



stretched through the air in front of an electric fan and carrying 1,600 

 watts. The relay controlling the heating current was burned by arch- 

 ing because it was too small and we did not obtain a large one in time. 

 But we found it possible to control the temperature to 0.1 by personal 

 attention to a sensitive thermometer (graduated in tenths of a degree) 

 placed in front of a one-sixth horse-power electric fan, and the heating 

 current was controlled by means of a push-button. 



The only time the electric heating failed to be sufficient was on two 

 successive days when we were required to finish the experiments at 30, 

 although the outdoor temperature was about 30 C. It was then 

 necessary to fill the space between the windows and dark curtains with 

 cotton batting and to turn on the steam heat. The radiator was 

 inclosed in a paper covering and a hole left in this of such size that the 

 temperature did not quite reach 30, but could be quickly raised to 30 

 by means of the electric regulation. It was necessary to keep a one- 

 sixth horse-power electric fan and one or two other fans blowing on the 

 apparatus all the time in order to keep all pieces of apparatus at 

 the same temperature. The experiments at 10 were postponed until 



