52 



Papers from the Department of Marine Biology. 



lowering the burette tip far enough into the hole in the top to seal with 

 a water seal. Hydrogen is passed through for about 15 minutes before 

 commencing the titration and is continued all through the titration, 

 escaping through the water seal, which should be replenished with a 

 drop of distilled water in case it is blown j^ 



out by the hydrogen. 



The most difficult problem was to bring 

 the sea-water in the hydrogen electrode 

 to a known CO2 tension. Various forms 

 of apparatus for treating the sea-water 

 with gas mixtures were tried, but it was 

 found that a very long time was required 



16 



Fig. 16. — Tonometer electrode for deter- 

 mining the Ph of sea-water at a pre- 

 determined COj tension. A mixture 

 of CO2 and H2 is bubbled through the 

 sea-water in a narrow tube; then the 

 stopcocks are closed and the electrode 

 inverted so that the sea-water flows 

 into the wide portion, which is of the 

 same bore as the colorimeter tubes, 

 so that the hydrogen electrode deter- 

 mination of the Ph naay be compared 

 with that by the colorimetric method. 

 The stopcock on the wide end of the 

 electrode is not greased, as it serves 

 for electrolytic connection with the 

 KCl bath. 



Fig. 17. — Gasometer for mixing CO2 in 

 ten-thousandth parts with H2 (atmos- 

 pheric pressure being insured by the 

 traps, 00). The apparatus holds 25 

 pounds of Hg and hence must be 

 bound with iron wire run through 

 boiling sealing-wax while being woimd 

 on diagonally. The narrow tube is 

 graduated in tenths or hundredths of 

 a cubic centimeter. The apparatus 

 holds 1 liter of gas when the mercury 

 meniscus is at AI. The proportions 

 are not quite correct in this figure. 

 It is best to have the apparatus nar- 

 rower and so that M may be marked 

 on the cylindrical part; or (as we 

 accomplished in one apparatus) M 

 may be at the lower stopcock. The 

 lower stopcock is connected by means 

 of a piece of pressure rubber tubing 

 to a leveling bulb held up by a rope 

 passing through pulley attached to 

 the ceiling. 



to reach equilibrium. We finally devised a simple apparatus in which 

 equiUbrium could be reached in 30 minutes or less (although we took 

 more time to make sure of it after the first time tests were made) . This 

 tonometer electrode (fig. 16) consists of a tube 450 mm. long and 7 mm. 



