Edward T. Radleyl
University of Missouri Columbia
A Simple Technique for Semimicro Volumetric GUS Analysis
The technique of injecting a liquid into a gas chamher by rolling a mercury globule over a fdm of the liquid in a capillary tube may be used to advantage in volumetric gas analysis. It is also useful in analysis where a gas is used as a reagent. The percentage by volume of a major component of a gaseous mixture can be determined by measuring the decrease in length of a column of the gas, trapped between two mercury globules in a uniform bore glass tube, upon exposure t o a suitable absorbent solution. A simple and interesting example of the technique is the determination of the per cent by volume of oxygen in the atmosphere. The author has consistently obtained a value of 20.9 =t0.1% by the procedure outlined below. A 40-cm column of air is trapped between twomercury globules in a 2 m m i.d. glass tube about a meter long. The tubing is placed flat on the table top and the distance between the globules is measured to the nearest mm while the column is near the right end of the tube. The column is then drawn almost to the left end of the tube and a few drops of pyrogallol absorbent solutionZ is introduced next t o the left mercury globule by means of a medicine dropper with a drawn out stem. The globules are next drawn about 30 cm toward the right and then forced back toward the left end of the tube. The left globule rolls over a film of the pyrogallol solution which is thus exposed to the entrapped gas column. A 20-cm length of this solution film between the globules will rapidly absorb the oxygen in the tube. After a few minutes exposure, the globules are again
Graduate student and N. S. F. Faculty Fellow, 1960-61.
' VOGEL,A R T ~ RI., "A Textbook of Quantitative Inorganic Analysis Theory and Practice," 2nd ed., Longmans, Green and Co., New York, 1951, p. 802.
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Journol o f Chemical Education
drawn into the right side of the tube until the left globule has rolled completely over the dark film of pyrogallol solution and the space between the globules is free of absorbent solution. The distance between the globules is again determined, after a few minutes to allow thermal equilibration, and the per cent by volume oxygen is computed. (It should be noted that any carbon dioxide present also reacts with the pyrogallol, and this is included in the "percentage of oxygen" thus obtained). The ratio between the decrease in length and the original length of the column is the fraction by volume of oxygen in the atmosphere. Care should be taken to avoid contact of pyrogallol solution with the skin, and the usual precautions should be observed in handling the small quantity of mercury. The sample tube may be filled with other gas samples by mild aspiration or low pressure flow through a fine capillary. The mercury globules may be introduced by placing a small quantity of mercury in the rubber tubing between the sample container and the measuring tube and raising the rubber tubing so that the mercury blocks the flow of gas and is forced into the measuring tube. Most of the conventional gas absorbent solutions have low vapor pressure a t room temperature and do not react rapidly with mercury. If the ahsorbent solution has an objectionably high vapor pressure, this may he determined by the method previously described by the author3 using an inert gas in the measuring tube, and an appropriate correction may be applied to the final length measurement. When it is desired to test for more than one component in the mixture, the measuring tube should terminate in a small spherical glass joint, to which a series of absorption tubes may be attached in succession, care being taken to prevent the absorbents from coming near this joint. a
RADLEY, EDWARD T., J. CHEM.EDUC., 37, 35 (1960).
