Inexpensive Pipet Filler
the system to be easily applied t o routine use by students. The system consists of a standard red rubber pipet bulb (most conveniently the 30-ml or 1-oz size), an ordinary glass medicine dropper barrel, and a 2-in. length of 5/16-in. 0.d. rubber tubing containing a glass or Teflon* bead (see figure). We have provided several tubinghead assemblies in laboratory desks, so that one may be attached toeoeh pipet inastudent loeker. To fill apipet, the bulb isdepressed, then the barrel inserted into the tubing and the pipet immersed in the fluid to he measured. The bead is then squeezed, drawing the fluid up into the pipet; releasing pressure on the head instantly stops inflow of liquid. After the pipet is filled and the bead pressure released, the bulb assembly is removed from the tubing and the fluid delivered by applying a~propriate pressure to the bead. Excellent pressure control is secured, during both filling and delivery oper.. . ations. The rubber bulbs may be purchased in quantity for about $1 each, while the dropper barrels are made from ordinary glass tubing. Short pieces of scrap rubber tubing and glass beads are generally easily located in any laboratory. A single bulb serves as many pipets as one wishes, while the tubinghead assembly provides a n additional advantage. Pipets may be stored filled with distilled water, since the tubinglbead assembly provides a seal until pressure isapplied to the bead, resultingin generally cleaner condition of student pipets than ordinarily may he the ease. 1
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Harris, W. E., and Kratoehvil,B., J. CHEM. EDUC., 53,253-4 (1976). Hanson, R. H., J. CHEM. EDUC., 54,434 (1977). Tatum, C. M., Jr., J. CHEM. EDUC., 55.38 (1978). Hickling, G. G., J. CHEM. EDUC., 355,541 (1978).
Ball State University Muneie, IN 47306
756 1 Journal of Chemical Education
Robert E. Van Atta Dwight 0.Kamback
