An Inexpensive Safety Device for Pipets Inexpensive rubber bulbs are often utilized in general chemistry labs to draw liquids into pipets, in lieu of the more expensive pipet bulbs wbicb are fitted witb ball valves. The essential feature of control provided by the more expensive device may be obtained simply by attaching a rubber bulb to a short length of glass tubing wbicb is connected to a 5-cm length of amber latex tubing into wbicb a glsss bead bas been inserted. (See figure). Squeezing the tubing to deform it in the region of the bead will permit air to pass around the bead in a controlled manner. In use, air is first expelled from the hulb through the tubing, the device attached to the pipet, and liquid drawn into the pipet by operating the glass valve. The liquid is discharged by first removing the bulb and then permitting air to enter the pipet through the valve. Insertion and removal of the hulb is facilitated if the glass connector between the hulb and tubing is tapered at the bulb end. A medicine dropper serves well. Students who have never used a pipet are able to perform safely, accurately, and more rapidly witb this device than when using the more conventional technique in which a finger is used directly an the pipet. We have found 30-ml rubber bulbs, 6 m m solid glass beads (obtainable from Fisher Scientific), and 3hs x Yts-in. amber latex tubing to be suitable components for use witb a 25-ml pipet. University of Georgia Athens,Georgia 30602
Gayland A. Dadd T. Cassen
Volume 51, Number 7. July 1974
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