Non-Flame Heat on a Budget Harold J. Teague Pembroke State University, Pembroke, NC 28372 Problems associated with flames in the organic laboratory are well known. To circumvent these problems, as well as problems associated with cost and frequent breakage of ground-glass equipment and the cost of chemicals and the disposal of them, our organic laboratory, as many schools are doing, switched from macroand semi-microscale to microscale between the fall and spring semesters of 1990-1991. Heat-Power Source One challenge was how to provide non-flame heat, which was deemed essential. The decision was made to use sand baths, as recommended for many microscale procedures ( I , 2). Specifically, a 100-mL Model C3AM Thermowell (3) heater to be filled a ~ ~ r o x i m a t e85% l v full with oualitv sand was decided up& as the he& source. The list price is $41.50 per unit, which we consider an outstanding value. How to power the Thermowell units next had to be addressed. LC1 (3) recommends one of nine models of their Powermite Heat Control series, which range in price from $53.50 to $80.00. However, we reached the conclusion that powering multiple Thermowell units with a single power source would be both cheaper and more effectivethan individual power units. The 1992 Thermowell product bulletin (3)provides information that supports our decision to power multiple units with a single power source. The 100-mL Thermowell is rated a t 140 W (120 V); however, when filled 85%full with sand the maximum power for continuous operation is 50% (83 V). At 40% power (75 V) and filled 85% full with sand the temperature gradient fromjust hdou, sand surface to n depth of25 mm will vary fmm about 280 'C tu 390 'C. Contmuous operation of a Thermowell sand bath at 4 W power does not produce critical heat in the unit. Based on above information (and our experience) a 100-mL Thermowell sand bath at 40% power; i.e., producing 56 W, provides a sand bath temperature range that is about ideal for the organic laboratory. Each 100-mLThermoweU(75V; 56 W) is expected to consume approximately 0.75 A. Therefore, a 10-A variable power transformer should be adequate to power a minimum of 13 100-mLThermowellsand bath units. Laboratory Set-up Our laboratom has four benches with four work stations on each side, foia total of 32 work stations. Therefore, four transformers, each powering eight Thermowell sand baths per bench, were deemed sufficient for our needs. A 10-A transformer can be purchased for $126.35 (4). However, we were fortunate enough to scavenge four unused transformers from storage, three of which had been donated to us as surplus property by a neighboring industry. The four units we use are as follows: A. One bamp, Type W5MT Variac unit, General Radio Ca., Concord. MA B. Two 10-amp,Type NllAB Powerstat units,The Superior
Electric Co., Bristol, CN
C. One 10-amp Type 3PN1010 unit, Staco Co., Dayton, OH
The set-up for our laboratory is arranged as follows: One transformer unit (figure,part A), connected to 110-Voutlet, is placed near the center of each of the four laboratory benches; to each of
Thermowell sand bath and power set-up (one bench). these units is plugged a six-outlet surge protector (local hardware, $17.95) (figure, part B) ; to each surge pmtedor is plugged four Thermowell sand baths (figure, part C) and two 9-ft. air conditioner cords (local, $6.95) part Dl; these mrds supply, t h n @ outlet adaptas O d , $2.59) (figure, pah El, two ThermoweU sand baths (fiw, part C) on each end of each laboratory bench. The cost for the four surge ~rotectors.eieht air conditioner cords, and eight outlet idaptem tdtalzd $148.12, or $4.63 oer station. If it had been necessaw to ~urchasefour auto kansformers, the cost would be $653.'52, or $20.42 Der station. which is still a considerable savinw over indikidual units. (For those willing to wi;e electrical outlet boxes and connect directly to the auto transformers much of the $148.12 can be saved!)
(m,
Operation The transformers remain set at 75 V On laboratory day approximately one hour before lab, or before briefing, the four transformem are switched on. When the student gets to the laboratory hidher Thermowell sand bath has reached maximum temperature and is ready for use. The student is not permitted t o alter any controls o r plugs. Summary We have gone through two semesters of microseale with this system, and it has worked beautifully It is advantageow to have all units at the same temperature; without contmls for the student to operate there is less worry of the units reaching critical heat and thus failure. Switching on the four transformers is a simple task that takes about 30 s. Comment. As indicated above one transformer (Variac) is rated a t 5 A. We have powered eight 100-mL Thermowell sand baths with this transformer (set a t 75 V) without ~roblem.This indicates to us that more than the calculatid 13 100-mI.Thermowell sand baths (75 V, 56 Wl can bc powered by onc 10-Atramformer. It is possible that a single 10-A transformer may be sufficient to power all the sand bath u ~ t required s by a small laboratory. Literature Cited I. wimamaon,K L. ~ ~ s c o l e.uhrnsrnk orgonic ~ ; r p r i n o n fneath: ~; ton,MA,1989. 2. Mayo, W M.; Pike, R.M.; Butcher, S. S M i c m i c k O~gonicLabomfory;W~lqi: New Y d ,1986. 3. Lahato?. C d m u r Inc, P 0.Box 148,Beloit, WI.53511. 4. Prey ScientificW658, P OBox 8101,Mansfield, OH M901.
Volume 71 Number 5 May 1994
435
