Magnetic Stirring Devices for Use with Overhead Projectors Overhead projectors could be used more conveniently for lecture demonstrations involving solution chemistry if it were possible to stir the a,lutirms easily. This paper describes three magnetic stirrers whichcan be used for this purpose. All three are hased on using the G. Frederick Smith Chemical Co. (GFS) magnetic stirrer.' The simplest version involves horingout a 3-in. hole most of the way througha piece ofPlexiglas that is 1in. thick and 7 in. square. T h e hole is bored near one edge. Slots are milled out for the nipples, and holes are drilled and tapped through the sides to hold the stirrer in place. T h e device is shown in Figure 1. T h e second version is shown in Figure 2. In a piece of Plexiglas that is 7 in. square and 31d in. thick a hole is bored campletely thmugh the center and counterbored to take two Plexiglas discs. One of the GFS stirrers is taken apart and the bearings, rotor, and magnet removed. T h e bearings are press fit into the two discs. A new rotor is machined from Plexiglas, a slot is machined fbr the magnet, and the pins from the old rotor press fit into the new rotor. A '14-in. end mill is used to machine the grooves in the rotor. T h e discs are glued into place securing the free-moving rotor. Inlet and outlet holes, 'is-in. diam., are drilled, and the ends are drilled and tapped far %-in. pipe threads t o take brass nipples. A mator-driven version is shown in Figure 3. To accommodate the motor and pulleys a piece of Plexiglas which is 1 in. thick and 8 in. square is used. The magnet is obtained by taking apart a GFS stirrer-this is the only source we could find far magnets of this size, shape and power. T h e central pulley houses the magnet and press fit bearings which fit into
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Figure 1. The GFS stirrer mounted in a Plexiglas plate. The Sare set screws which hold thestimer in place.
Figure 2. A Plexiglas rotor R containing a milled-out section for the magnet Ma is set inthe plate. The S are bearings from a GFS stirrer and the Nare hose nipples with '/&. pipe threads.
BOTTOM WEW
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Figure 3. Ma is the magnet, the Pare pulleys(for an O-ring drive belt which is not shown), the Sare set Screws for holding the motor Mo in place, and the Bare miniature ball bearings.
miniature ball bearings in the bottom plate and the top surface. T h e top surface is one piece and the bottom plate is held in place with three screws. A channel is milled for the O-ring which serves as a drive belt between the small DC motor and the magnet pulley. Suitable DC motors are available from Edmund Scientific Co. or the American Science Center. The motor is mounted from the top surface and held in place with two set screws. We have fnund that the best kind of containers to use for demonstrations are crystallizing dishes which have flat bottoms and straight, hut low, walls. For example, the 170 X 90 (mm) dish conveniently covers any of our stirrers. Strongly colored soluticms can he used in shallow layers. Titrations and one-pot reactions, amongst others, are conveniently demonstrated using these stirring devices.
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This magnetic stirrer is available from SGA Scientific, Inc. Bloomfield, N.J., as #5-6962 for about $12.00. I t operates on air, water (or vacuum. Wright S t a t e University Dayton, O H 45435
184 / Journal of Chemical Education
Rubin Battino Howard R. D u F o u r J o h n L. Scott
