The Hydrogen-ion Concentration, etc., of Sea-Water. 



51 



allowing the solution to rise in it by gravity and blowing it out with 

 hydrogen. It is most convenient to make the vessel for holding the 

 sea-water with a ground joint at the bottom for electrolytic connection. 

 Select a glass-stoppered bottle, whose stopper does not leak, and cut 

 off the bottom. This is done by cutting a short groove with a file or 

 glass knife, and holding a heated rod just beyond each end of the cut 

 until a crack is started. One heated rod is moved over the line chosen 

 for the cut, at such a rate that the crack follows the rod. If metal rods 



14 



15 



FIG. 13. Hydrogen electrode that can be placed in the colorimeter for calibrating the colori- 

 metric method of determining the P H , being of the same bore as the sealed colorimetric tubes. 

 The ground joint at the bottom should not be greased, as it is for the electrolytic connection 

 with the calomel electrode through the interposition of a KC1 bath. The black circle ia a 

 palladized or platinized gold disk welded to a platinum wire fused through the glass. The 

 long narrow tube is for the introduction of a continuous stream of hydrogen which escapes at 

 the top through a trap which prevents the backward diffusion of air. 



FIG. 14. Dipping hydrogen electrode for titrations. Insert a drop of Hg and copper wire in W. 

 The bulb D is immersed in the fluid in an inverted glass-stoppered bottle with the bottom 

 cut off. The ground joint at the stopper serves for electrolytic connection with the KC1 

 bath. The cock C is turned so that the bulb D fills by gravity with the fluid, which 

 drives out the hydrogen at the trap T. Hydrogen is allowed to bubble through again and 

 the fluid allowed to rise until it just touches the palladized gold disk shown in black, when the 

 reading is taken. (From Jour. Biol. Chem., 1916, xxvm, 135.) 



FIG. 15. Hydrogen electrode for COz-free electrometric titrations. The principles of construc- 

 tion are the same as in figure 13, except that the trap at the top is made to admit a burette 

 tip, and can be sealed with a drop of distilled water after the burette tip has been inserted so 

 as to leave only a very narrow opening. 



or large nails can not be obtained, pieces of glass heated to a red heat 

 on the end will do. After removal of the bottom the bottle is inverted 

 and immersed to the neck in the KC1 vessel. In making the titration, 

 the sea-water is pipetted into the bottle and covered with a paraffined 

 cardboard with holes for the electrode and burette tip. 



A more convenient form of titration electrode is shown in figure 15. 

 It has the advantage that the air is excluded from the whole solution by 



