An Improved Mercury-Sealed Micro Absorption Tube REX J. ROBINSON AND DONALD J. DOANl University of Washington, Seattle, Wash.
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FIGURE 1. IMPROVED ABSORPTION TUBE
be broken momentarily and air sucked in before the seal again fell into place. Normally this does not happen and the slightly different buoyancy is compensated by making the blank determination with the identical technique. It is impossible for the mercury droplets t o be sucked into the tube; this objectionable feature is restricted to the Cornwell type of tube. In view of the normal tendency of the tube to cool before the weighing is made, this is an important point; on the other hand, if‘the sealed tube should be heated, the mercury seals may be expelled. Therefore after sealing the tube, i t should be handled only outside the seals, as otherwise the heat from the hands can easily expand the gas and expel the mercury. It is possible that extreme changes in temperature or barometric pressure from day to day may cause expulsion of the seals, though this has never occurred in the authors’ laboratories. The tube described above has several other important advantages. Simple rotation through an angle of 180” makes or breaks the seals; no shaking is needed as with other mercury-sealed tubes. The tube is inexpensively constructed and the simple design permits it to be made even by a relatively inexperienced glass blower. These are decided advantages, particularly when the tubes are to be used for class instruction where ease of operation is especially desirable and the breakage is likely to be great.
oxygen by air before the weighing is made. The use of a tube whose ends may be closed permits weighing while the tube is filled with oxygen and eliminates that part of the procedure dealing with the oxygen removal. This has been accomplished by fitting the tube with stopcocks (1,S ) , with mercury seals (2, 6),or with steel balls (4). Tubes with stopcocks have several important disadvantages. There is always the possibility of leakage around the stopcocks, accurate weighing is difficult because the tubes are heavy, the lubricant around the joints may pick up dust or moisture from the air, or some of the lubricant may be squeezed out and removed during wiping. Absorption tubes with mercury seals have none of these difficulties and still retain the advantage of weighing the tube without first displacing the oxygen with air. However, after the tube is sealed the mercury droplets may be dislodged if either the internal gas pressure of the tube or the atmospheric pressure changes greatly. Principally for this reason a tube sealed with stainless-steel balls was designed by Johns and found to be highly successful. The authors have used mercury-sealed tubes successfully for 10 years and feel that dislodgment of the seals by changing gas pressure need not be an important factor with tubes of proper design. Several types of tubes have been used in this laboratory, but the design which has given the most satisfactory results is shown in Figure 1. It was made from a Pregl tube which had been purchased from a commercial supply house. Bulbs 3.0 to 3.5 cm. in diameter were blown in the capillary tubing at the positions shown. Tubing 3.0 t o 3.5 mm. in external diameter was joined to the side of the bulb and bent as indicated, and at the junction of the tubing and the bulb a constriction about 0.25 mm. in diameter was made. This is small enough to retain the globule of mercury (2 to 3 mm. in diameter) which rests there when the tube is sealed, but large enough t o permit the flow of oxygen through the unsealed tube when in use in the absorption train. 1
Literature Cited (1) Blumer, F., Ber., 50, 1710 (1917). (2) Cornwell, R. T. K., IND. ENG.CHEM.,Anal. Ed., 3,4 (1931). (3) Flaschentrager, B., 2. angew. Chem., 39, 717 (1926). (4) Johns, I. B., “Improved Absorption Apparatus for the CarbonHydrogen Analysis”, presented before the Microchemical Section, American Chemical Society, Dallas, Texas, April, 1938. ( 5 ) Kemmerer, G., and Hallett, L. T., IND. ENG. CHEM., 19, 173 (1927). (6) Roth, H., and Daw, E. B., “Quantitative Organic Microanalysis of Frits Pregl”, p. 28, Philadelphia, P. Blakiston’s Son & Co., 1937.
Present address, The Eagle-Picher Lead Company, Joplin, Mo.
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