New Apparatus for Electrometric Determination of Hydrogen-Ion Concentration and for Gas Analysis

hydrogen, cc, sea-water, electrode and minutes

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An experiment designed to illustrate this was made as follows: 5 c.c. of sea-water were placed in the hydrogen electrode and a stream of pure hydrogen of about 100 c.c. per minute passed through it. About 15 minutes were required for saturation of the water with hydrogen (so that the P. was the same, 8.2, as with stagnant hydrogen, but with the electrode raised out of the water), and this time and 10 minutes more were counted out of the experiment. The water now contained 0.2 c.c. of in the form of carbonates and bicarbonates, calculated from the P. of 8.3. In 10 minutes, with the passage of 1,000 c.c. of H2 in small bubbles, the P. rose to 8.4, indicating that 0.007 c.c. of had been removed. The rate of removal constantly decreased in an asymptotic curve, and at the end of 2 hours a P. of 9 was reached, indicating that a total of 0.05 c.c. of had been removed. During the next 10 minutes the P. rose to 9.02, indicating the further loss of 0.0014 c.c. of At the end of 270 minutes the P. had reached 9.18 and was rising at the rate of 0.01 in 10 minutes, indicating a total loss of 0.0616 c.c. and a final rate of 0.0007 c.c. per 10 minutes.

There was still enough CO2 in the sea-water to convert most of the excess base into normal carbonate. This shows the hopelessness of reaching equilibrium at very low tensions, and we seldom attempted anything lower than 0.0002 atmosphere, and then made tests to see that equilibrium was attained within the limit of error of measurement. The buffer mixtures were intended to be and similar experiments on them showed that if traces of 002 were in them they were not removed by hours of bubbling hydrogen through them.

We know of no attempts to determine the asymptote or limit that is approached in the above experiment. If it is an NaOH solution that is approached, we should be able to remove any traces of from the buffer mixture (theoretically with ideal apparatus). The weak acid in the buffer should help displace CO2. Perhaps the reason we could not reach a higher P. by bubbling Hs through the buffer mixture was that the traces of CO2 were not sufficient to measurably change the P.. The electrodes for comparing the colors of the buffer mixtures and sea-water of the same P. were made of the same bore as the sealed tubes and so that they could be placed in the colorimeter after determin ing the P. electrometrically. The essential form of these is shown in figure 13. There are no ground joints or rubber connections exposed to the air. The hydrogen is allowed to escape through the trap at the top, which is filled with some of the same solution as in the electrode. Electrolytic connection with the calomel electrode is made through the ground joint at the bottom submerged in an intermediate vessel of saturated KC1 solution.

Some of the electrometric titrations were made with the dipping electrode shown in figure 14, which is rinsed with the solution by 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 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 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 out by the hydrogen.

The most difficult problem was to bring the sea-water in the hydrogen electrode to a known 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 to reach equilibrium. We finally devised a simple apparatus in which equilibrium 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.

bore with a stopcock at one end and the other end fused to a short tube of exactly 24 nun. bore, containing the palladized gold disk and closed with a minute ungreased stopcock. About 11 to 12 c.c. of sea-water contain ing the indicator were sucked up into it and it was clamped with the small tube downward (which then contained a column 30 cm. high of sea-water). The mixture of and HE was passed in at the bottom in small bubbles, and the flow regulated so that the sea-water did not rise into the large tube. The gas mixture escaped at the top through a trap connected to the stopcock by a short rubber tube, to prevent the backward diffusion of air. The gas pressure of the. bubbles varied from the barometer reading to the barometer + 300 mm. of water, the average being barometer 150 mm. of water or about barometer + 11.5 mm. of mercury.

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