Sealed, Inert, Gas Circulating Pump W. A. McAllister, W. V. Southerland, and G . B. Rouse, Jr. Department of Chemistry, East Carolina University, Greenville, M.C. 27834 IN A STUDY AT THIS LABORATORY involving the catalysis of the oxidation-reduction reaction between carbon monoxide and nitric oxide, an inert, leak-proof, gas circulating pump was needed. The gases are contained in a closed glass loop with the catalyst in a U-tube portion of the loop. The gases must be circulated slowly and continuously for days, and the rate of circulation must be reproducible, relative to gas pressure and impeller speed. A centrifugal design was adopted because of its inherent simplicity. The circular motions for such a design can be transmitted without mechanical connection using a magnetic stirrer, allowing the pump to be completely sealed. The other primary requirement is that the pump be unreactive and have no catalytic effect with respect to the gases studied. In this design, shown in Figure 1, the gases only contact glass, Teflon (DuPont), and Apiezon Wax (James G. Biddle Company, Plymouth Meeting, Pa.). The wax is used for a seal because it is inert and easily removable for cleaning the pump. Epoxy glue could be used for a permanent seal. For ease of construction, the pump was designed around the 7I8-inch “Roto-Stirrer” obtained from the Lab Apparatus Company (Catalog No. 2495). This seemed to be the least expensive of the several possibilities considered. The only critical construction details are to arrange the stirrer close to the top glass disk, and the tangential angle of the outlet. The perforated glass disk is not critical and can be replaced by a disk with a central 12-mm hole. This disk is fused in place but could be epoxied. The Teflon disk is simply a bearing surface. The result of this simple approach is a maximum gas circulation rate of about 10 ml per minute. Since this is not a positive displacement pump ( I , 2), it is difficult t o (1) C. J. Sterner. Rea. Sci. Iustrum., 31, 1159 (1960). (2) M. J. Hiza and A. G. Duncan, ibid.,40,513 (1969).
Figure 1. Sealed, inert, gas circulating pump measure circulation rates L‘S. revolutions per minute. The approximate rate was determined by observing the movement of NOn in the system. The pump operates in a range of pressures from a vacuum to one atmosphere; of course, circulation rates also depend on pressure. ACKNOWLEDGMENT
Thanks are due Owen Kingsbury for his patience and glassblowing skill. RECEIVED for review March 6, 1972. Accepted June 21, 1972. We thank the Environmental Protection Agency and the North Carolina Board of Science and Technology for financial support.
Improved Ebullator for Solution Concentrator Morton Beroza, Malcolm C. Bowman, and Barbara A. Bier1 US.Department of Agriculture, Agricultural Research Sercice, Beltsaille, Md. 20705 and Tfton, Ga. 31 794 A DEVICE,particularly useful in pesticide residue for simultaneously concentrating many solutions in test tubes to small volumes ( I ) , is presently available in a much improved form from Kontes Glass Co. Concentration is rapid until the solution reaches a low level, at which point evaporation slows markedly because the last 0.5 to 1.0 ml is below the heating zone of the evaporator block. Thus, losses of pesticide resulting from inadvertent evaporation to dryness ( 2 ) are avoided, and very little attention of the analyst is required in overseeing this normally time-consuming operation. ~-
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(1) M. Beroza and M. C. Bowman, ANAL.CHEM.. 39. 1200 (1967). (2) J. A. Burke. P. A. Mills, and D. C . Bostwick, J. Ass. Ofic: Ana/. Chem.. 49,999 (1966).
With this device, boiling of a solution is initiated by a n ebullator, which is a small glass rod bent so the open end of a n attached short length of tubing faces downward ( I ) ; the trapped pocket of air initiates and maintains ebullition. See K of Figure 1. The use of small-bore stainless steel needlestock tubing to direct a stream of micro-bubbles of nitrogen through the solution for ebullition has significant advantages over the glass ebullator used originally. As noted before ( I ) , benzene tends to bump and some shaking of the test (or other distilling) tube is necessary to start boiling with the original ebullator; with the stream of N B ,benzene is smoothly concentrated without bumping. If heating should be interrupted, as is sometimes necessary, the solution being concentrated fills the little air
ANALYTICAL CHEMISTRY, VOL. 44, NO. 14, DECEMBER 1972
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