Bernard Miller American University Washington, D. C.
Multiple Remote Magnetic Stirring Device
In the course of experimental studies on the movement of macromolecules through liquid-liquid interfaces, we have found it necessary to drive stirrer bars which were in glass cells set in thermostated water baths. The available electrically powered driving units are not capable of operating under water and produce a considerable amount of undesirable heat when running continuously. To provide suitable stirring, wc devised an arrangement by which rotary motion from a motor was transmitted through flexible power cables to magnets fixed to the ends of the cables. The magnet ends of the cables were then placed as needed in the water baths and provided the necessary drive for the stirring bars without any appreciable heat effecton the bath. The motor was a hp, gear-reduced, Bodine model with high torque and variable low speed. Its driveshaft was connected through a three-piece flexible coupling to one of five parallel-mounted shafts. Each of the latter included a gear meshing with its neighbors, so that all five shafts would rotate at'the same speed. Each shaft was connected to a hollow fitting designed to hold the end of a flexible power cable. The cables were standard automobile speedometer cables, purchased for about $2 each. Small bridge or horseshoe magnets were cemented onto one-hole rubber stoppers and the outer exposed shafts of the cables were cemented into the holes in the stoppers. The resulting apparatus thus was capable of performing five separate magnetic stirring actions. The driving magnets could be placed under water a t any angle and no motor heat was transmitted to the materials being stirred. The cost per stirring unit was about $13.50 in this case, and would be even lower if more shafts were driven by the same motor. This makes this
arrangement considerably less costly than conventional units. The removal of the driving motor from a region where a variety of chen~icalsare being processed should also help prolong the life of the apparatus. Our unit has been operating continuously for 18 months without any significant trouble. The particular arrangement described above is only one of several alternate ways to bring about this kind of remote magnetic stirring. Other flexible power cables are available which might prove to be better than the speedometer cables. (The latter contained an internal lubricant which contaminated the water baths until it was washed out.) I n laboratories where there is much magnetic stirring, it might be practical to have a built-in console drive unit with plug-in points for the cables. The construction and design of the particular unit described here was mainly the work of Mr. Neil A. Muncy and was built for experimental work supported by Public Health Service research grant No. Gi\I-9505. The illustration is by Francis M. Roberts
Volume 42, Number 7 7, November 7 965
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