236 Papers from the Department of Marine Biology. 



photosynthesis in the symbiotic plant cells. Time was measured by 

 means of a stop-watch and a clock. The same cassiopea was used in a 

 series of experiments. 



The oxygen in the sea-water was determined by the Winkler method, 

 which can be corrected for the small error due to a slight amount of 

 organic matter given out by Cassiopea, and it was thought impracticable 

 to use the complicated method of Shutzenberger and Risler (Henze, 

 19106). A 250 c.c. glass-stoppered bottle was weighed empty and full 

 of distilled water at a known temperature, in order to standardize its 

 volume. It was fitted with a double-bored rubber stopper and a long 

 and a short glass tube with rubber connections. The bottle was filled 

 with mercury and the long glass tube was sucked full of the water to 

 be analyzed and the stopper inserted. By inverting the bottle the 

 sea-water was siphoned into it, when the rubber stopper was removed 

 and the glass stopper inserted. The glass stopper was lifted and 1 c.c. 

 of alkaline KI solution and 1 c.c. of 40 per cent MnCl 2 solution intro- 

 duced (correction being made for this in the O 2 calculation) and the 

 stopper was inserted. Colloidal membranes formed about the drops of 

 alkali and violent shaking was necessary to break them. After the 

 precipitate had settled, 2 c.c. of concentrated HC1 were added and the 

 stopper inserted and the bottle shaken. Its contents were transferred 

 to a flask and titrated with 0.01 N sodium thiosulphate solution until 

 the yellow color disappeared ; then starch solution was added and the 

 titration continued until the blue color disappeared; then the water 

 was poured into the bottle and back into the flask and titrated until the 

 blue color disappeared. The calculation was as follows: 



0.056 X c.c. thiosulphate ,, ,., c 



- = c.c. of oxygen per liter ot sea-water 

 capacity of bottle 2 



and this quotient multiplied by 0.9 equals cubic centimeters of oxygen 

 in calorimeter (on the assumption that the concentration of oxygen in 

 the cassiopea was the same as that in the sea- water). 



In order to reduce the carbonate content, the alkaline KI solution 

 wae made fresh every few days from two stock solutions. Carbonate- 

 free NaOH solution was made by dissolving 100 grams of NaOH in 

 100 c.c. H 2 O in a glass-stoppered bottle and pipetting off after the car- 

 bonate had settled. One part of this was mixed with one part of 20 

 per cent KI solution before being used. NaOH made from metallic 

 sodium contained a trace of nitrite and NaOH purified by alcohol con- 

 tained but little more. This nitrite causes no error if the titration is 

 quickly made immediately after adding the acid, but the contents 

 of the flask slowly turn blue for hours after the end-point has been 

 reached. If the acidity is greatly increased, however, the nitrite causes 

 an appreciable error in the titration. 



The MnCl 2 solution contained a trace of Mn(OH) 3 , but this was 

 removed by decantation. The thiosulphate was dissolved in CO 2 -free 



