A Stirrer for a Constant Temperature Bath For several years we have been operating constant temperature baths with about 200 1capacity. Several types of commercial laboratory stirrers have been used. However, in continuous operation the bearings wear excessively so that the stirrers become noisy and unreliable. Even more serious is the comparatively small stirring rate. We have found a more satisfactory bath stirrer t o be a commercial sumo DUmD. (Model 500 SPV, with a brass im~eller.made bv Wavne Home E a u i ~ m e n t Company, Inc., Fort Wayne, ~ndiana;has been satisfactory.) I t is nomore eape&ve than a good laboratory stirre; but circulates the bath liquid a t a much higher velocity. Initially the outlet of the sump pump was fitted with an 1%-in.vertical pipe with a 1-in. wide slot about 8-in. long cut in the side of the pipe to serve as discharge port while the top end of the pipe was capped a t the surface of the hath liquid. More recently a 10-in. length of 4-in. diameter copper tubing was fastened t o the outlet of the sump pump. Within the copper tube has been placed a 20-ft Length of Ks-in. copper tubing coiled for circulating cold water and an 800 watt coil of resistance wire for heating. A length of 1%-in.copper tube slotted along one side and fitted to the top of the copper tubing heat exchanger orovides the discharee from the DUmD that stirs the bath. With this sumD at combination. bath tem. .D U ~.D - h e exchaneer ;rraturei are conitait within O.lOlO(; throughour rhr barh. The temperature conrrol has be& provided by arhermistor cmnrcttd 10 a pmp~rtionalcontruller while temperatures have been measured wirh a platinum rrsisranre thermometer and bridge. Laurence E. Strong Earlham College Richmond. Indiana 47374
Volume 53, Number 9, September 1976 / 585
