An Inexpensive Magnetic Stirrer Faced with the need t o perform titrations in the field in connection with water pollution studies, we required a portable magnetic stirrer. These do not appear to be readily available commercially and so we constructed one as follows. A Volkswagen windshield wiper motor (6V in pre-1968 models) was purchased from an auto wrecking yard and the outer case and final drive cog with attached orbital axle were removed. A l-in. bridge magnet (A) was cemented (Araldite epoxy) into a U-shaped holder (B) which was soldered to a %-in. length of copper tubing (C). This was connected t o the outermost cog ( D ) by means of Araldite and a %-in. length of plastic tubing ( E ) . The motor was bolted through four existing holes onto two aluminium strips (F) and (GI,the ends of which in turn were screwedta the top (HI of the stirrer case. The latter was of %-in. chipboard with a 1% in. dia. hole in it to accommodate the bridge magnet. A clearance of 'k in. was allowed between the magnet face and the white Formica plastic top (I). Two sides of the box were of %-in. chipboard and onto these were screwed the other sides of 'js-in. plywood. The motor was connected via a switch and terminals mounted on the side of the boa to a 6-V, l l - A hr motorcycle battery. Because of its gearing, the motor has a high torque and rotates the magnet a t a constant speed of ca. 250 r.p.m. The motor draws a current of about 1 amp, giving about 10 hr of use before recharging of the battery is necessary. The external dimensions of the stirrer are 5 in. x 5 in. x 4 in. and the weight is about 1.8lbs. The total cost of the stirrer (excluding battery) was less than $3. 'To whom inquiries should he addressed.
J. Ellis' S. Kanamori
Wollongong University College Wollongong, N.S.W., 2500, Australia
Volume 50,Number 2, February 1973 / 137
