Determination of Oxygen in Tank Hydrogen HUBERT N. ALYEA, Princeton University, Princeton, N. J.
I
Bulb G rests in an ordinary ring. CE is filled with mercury and D with water. Bulb C and manometer E must be kept clean and dry at all times.
N RESEARCH employing tank hydrogen i t is often desirable to determine the presence of traces of oxygen. A
method is here described for measuring these traces with a n error of less than 10 per cent for oxygen concentrations of 0.05 to 0.20 per cent b y volume. While the principle involved is far from new ( I ) , the apparatus shown in the figure is considerably simpler and more accurate than those previously described. I n principle, the traces of oxygen are burned with hydrogen on a glowing platinum wire. The water which forms condenses, thereby effecting a disappearance of three volumes, two of hydrogen and one of oxygen, for each volume of oxygen originally present. APPARATUS.The whole apparatus is mounted on a wooden base 37.5 X 25 cm. (15 X 10 inches) with a backboard of the same dimensions. Bulbs C, D, F , and G are all of 100-ml. caThe slanting manometer, E, is of 2-mm. capillary tubing astened to a 20-cm. length of meter stick, which is inclined to give a drop of 2 cm. over its 20-cm. length. A capillary stopcock may be conveniently inserted at E, although this is not essential. The water jacket surrounding C is made of 50-mm. tubing and a cork. A rubber stopper, rather than a glass-tungsten seal, is provided for the ignition vessel, D, so that the platinum wire can be easily replaced if burned out. Two stout tungsten lead-in wires are insulated from each other by a 5-mm. glass tubing, not shown, which is embedded in the rubber stopper and extends up over one wire to the platinum coil. The platinum spiral is made from No. 28 wire, 20 em. long. A scratch is made on BD about 3 cm. from B. A and B are small, two-way capillary stopcocks. Section AZ should be bent out from the board. Leveling bulb F is set in a 5 X 5 cm. (2 X 2 inches) wooden block, hollowed out and filled with plaster of Paris, so that F may be returned to exactly the same position each time. The block is fastened to a rod which may be clamped into position.
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rity
PRELIMINARY OPERATIOXS. The residual air in the apparatus must first be replaced by tank hydrogen. Once this has been attained the steps in this section may be omitted. Open passage DBI and raise G until the water nearly reaches B. Open passage CBI and raise F until the mercury gushes into BZ. Excess mercury may be caught in a beaker held at I . Attach the hydrogen sample a t H , open HAZ, and flush out with the hydrogen. Then turn the cocks to open passages HABC, filling C with hydrogen. Flush out the residual air in BD by opening CDB, running in hydrogen bv raising F or lowering G, and finally opening DBAI and CBAZ. Both water and mercury will now be a few centimeters from B, and the tiny volume of gas
between them will be nearly pure hydrogen. Therefore all subsequent measurements may omit these preliminary operations. MAKING AN AXALYSIS. Open CBAZ, and raise F to empty the gas out of CB until mercury again spills out a t I . Open HAZ to flush stopcock; then open HABC and run in the sample to be analyzed, stopping when the mercury reaches a point near E on the manometer. At this point, switch to HAZ, and finally close READINGS ON MIXTURES TABLE I. CONSECUTIVE Com osition of Gas by Volume Hylrogen
Oxygen
%
% 0,051
99.949 99.900 99.864 99.937 99.906
104
0.100 0.136 0.063 0,094
Movement in Manometer Mm. 27 48
70 30
50
Oxygen Found % 0 OS4 0 096 0.140 0.060 0.100
ANALYTICAL EDITION
February 15, 1941
stop cocks A and B. Record the position of the mercury on the manometer scale. Open passage CBD, and run the sample over into D. stomine when the mercurv is a few centimeters from B. The witkr revel will be well bdow the platinum wire. Close B and switch on the electricity, keeping the platinum spiral heated to a dull red, not white, heat. With hydrogen containing about 0.05 per cent oxygen 10 seconds are sufficient; for 0.20 per cent oxygen heat for -1 minute, but never any longer. Allow the gas to cool for 2 minutes, return it to C, stopping the water a t the scratch 3 em. from B , and record the new manometer reading. The calibration of the manometer can be calculated from its
105
slant, but it is simpler to make a direct measurement with empirical mixtures of oxygen and hydrogen. Table I shows that a movement of the mercury along 1 mm. of the manometercorresponds to 0,002 per centof oxygen by in the
Literature Cited (1) Ambler,
H.R.,Analyst, 55, 677 (1930).
Tungsten-Nickel and Tungsten-Silver Electrode Systems in Neutralizations HAROLD G. DIETRICH AND PAUL J . BENDER Sterling Chemistry Laboratory, Yale University, New Haven, Conn.
mended tungsten as an indicator electrode for neutralizations, and among the bimetallic electrode systems suggested by these investigators for such reactions are tungsten-nickel and tungsten-silver. After a precise study of the tungstennickel system in neutralizations Furman and Low ( 3 ) reported this system of value in titrations of strong acid with strong base, and vice versa, for solutions 0.1 11' and above. According to their observations nickel undergoes an abrupt change in potential at a pH about that a t which the transition of methyl orange occurs, but is relatively insen$tive in the region a t which phenolphthalein changes. It is the purpose of the present paper to show that these characteristics of the nickel electrode make the tungstennickel pair unsuitable for precise work in the titration of solutions as dilute as 0.01 S,and to describe the results of a detailed study of the tungsten-silver system in neutralizations involving solutions the approximate concentrations of which are between ATand 0.001 S.
Materials and Procedure Solutions of about the normality desired were prepared from reagents of analytical grade, the alkali solutions being nearly free of carbonate and the usual precautions being taken to protect them from atmospheric carbon dioxide. Electrodes w r e of the following 13. 8r S. wire gages: tungsten, 19; nickel, S and 24; silver, 24. After each titration the electrodes were cleaned with sandpaper, then washed with 6 A: nitric acid and several changes of distilled water. Occasional omission of the nitric acid washing seemed to have no bearing upon the results. A definite volume, between 15 and 40 ml., of the solution to be titrated was placed in a closed container and the neutralization was carried out a t room temperature in an atmosphere of nitrogen free of carbon dioxide. While the solution was being stirred by a motor-driven stirrer, the course of the titration mas followed by means of a Leeds Bt Korthrup students' type potentiometer and accessories. Readings were taken after the e. m. f. appeared virtually constant. I n the neighborhood of the end point these were recorded after each drop of the solution JTas added. The maximum of the A e. m. f./ A ml. was taken as the electrometric end point and compared nith end points obtained either simultaneouslv or indeDendentlv with DhenolDhthalein. methvl orange. or mkthvl red indicators. The 'color c'hange foi methj.1 red \Gas made mo're distinctive by the presence of rnzthylene blue. Each of the end-point ratios (ml. of acid per ml. of
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