A Convenient Glassware Cleaning Bath Over the last few years a method has evolved in our laboratory which provides truly clean glassware with minimal effort and apparatus. Although originally designed for a biochemical research laboratory where traces of metallic ions could not he tolerated, the method has become favored in student laboratories as well. The procedure involves mechanically removing any hulk dirt from the glassware, completely immersing the glassware in 0.25% PEX cleaner, heating for several hours, rinsing several times in tap water and then in deionized water, and drying in an oven. A major drawback of this procedure bas been the lack of a convenient, reliable heating hath. A vertically mounted electrical immersion heater rewires a stirrer, often melts olasticware which floatsinto the heater. and sometimes even damaees ~. thc heamp: t u b A stram immersiun hcatcr r o w r u r t r d ui hrar-re;lrtant nunmctallir tuling swkls these prohlcms but ir \ e n rxpmtiw and lartsonly n tcw months. A n external hrater, iurh as a hutpla~c,rannot tw used nitha plastic tub. h thc shorlnrn~ingiof prrvh,uxd~.icn. IS dcscribrd here. structirm uf a hwting hath w h ~ avoids ~
#ll STOPPER
@UB
Scale drawing of the horizontal immersion heater far the glassware cleaning bath.
The hath consists of a 30-gal. polyethylene tub, a homemade 1000-W immersion heater, and a 24-hr timer. Six inches of insulation are removed from a 5-ft section of 1812 heater ("lamp") cord (with plug). An uninsulated, solderless connector is used to attach one end of an l l - f t piece of %gauge Chromel wire (total resistance = 10.7 ohms) to one of the heater cord wires. The connected wires are slipped into a 12 X 318 in. O.D. Vycor tuhe and the majority of the Chromel wire wound around the outside of the tube to form a 6 - i d o n g heater coil. The other end of the Chromel wire is then attached to the other heater cord wire and the solderless connector pounded flat. The entire heater assembly is then slipped inside an 11X 5h-in. O.D. Vycor tuhe which has been sealed at one end. This assembly, in turn, is inserted into a hole ( # I 0 borer) in a #11 Neoprene stopper as shown in the figure. Note that the Vycor tuhesare arranged so that the uninsulated portions of the heater cord wires cannot touch. The heater is pushed firmly into a 2-in.-diameter hole which is drilled just above the bottom of the tube. A cap of PVC pipe fittings is notched to accommodate the heater cord and pushed onto the Neoprene stopper to protect the bare wires. To protect the Vycor tubes from heavy glassware, a rigid plastic grill (a refrigerator pop can dispenser manufactured by Rubhermaid) is epoxied to the bottom of the tub. Setting the time to heat for 2.5 hr provides a maximum temperature of about 75°C (except far a region within '12 in. of the tub hottom) and yields truly clean glassware. Tom Lyons Fisher Phyllis M. McGinnis Juniata College Huntingdon, PA 16652
82
Journal of Chemical Education
