Some like it hot

Topeka, Kansas 66621. Some Like It Hot. Sheldon H. Cohen. Washburn University of Topeka. Topeka, K$ 66621. Heating is one of themost fundamental ...
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Washburn University Tooeka.Kansas66621

Some Like It Hot Sheldon H. Cohen Washburn Unlverslty of Topeka Topeka. KS 66621

Heating is one of the most fundamental operations in a chemistry laboratory. Fortunately, burners are still relatively inexpensive and can be easily purchased from commercial sources. However, other techniques which require the input of energy, such asthe heating of;nflammahle organic liquids and the removal of a solvent at a temperature below its boil in^ point, require expensive sprcid rquipmcnt. This rolumn will rr\.it.w three de\icei tram earlier iswri uil'lllSclOllRN.lI.Ih;u can be helpful in solving some of these special heating problems. A Light Bulb Hot Plate A hot plate is an extremely useful piece of apparatus, hut they cost from $30 to over $100 each. A good substitute for all those jobs which require temperatures of not over 70°C is a light bulb hot plate which was proposed by Leonard Kreider ( I ). A diagram of a modifed version of his heater is given in Figure 1. Construction is simple and can he done in about three hours. Most of the items (tin can, metal strips, wire gauze and wood base) were obtained without any cost by using scraps. The electrical cord and the precelain light socket were purchased a t a local hardware store for a total of $2. This expense compares favorably with the 1935 original price tag for parts of $0.50. The device is excellent for keeping water a t a relatively constant temperature (raising the height of the beaker from the light bulb lowers the liquid temperature), and for the removal of low-boiling organic solvents from open vessels. In the later case the precaution of making sure there is good exhaust hood ventilation and no flames near the heaker are extremely important. Electric Flask Heater The distillation of volatile liquids from round-bottom distilling flasks is hest done with heating mantles, but, unfortunately, these useful devices cost from $25 to $50 apiece. An inexpensive substitute for heating mantles was described by Frederick Mathews (2).The electric flask heater is illustrated along with the other equipment discussed in this column in Figure 2. The starting materials needed are a coffee can, two glass insulators (short pieces of laboratory glass tubing), coiled resistance wire (the length will vary with the size of the wire available, but in our example 12 f t of B S No. 24 Nichrome wire was used), and plumber's cement (available from any local heating contractor). For details of the construction it is best to refer to the original article (2).The total time for this preparation was about two hours, not including the time needed for drying the cement. The expenses were about $1.25 for the heating wire and $0.75 for the plumber's cement. One very important caution is needed. This heater can not be plugged directly into a 110-V outlet, but instead i t uses a variable transformer. Since these cost about $50 each, our low cost device may not appear very useful. However, this leads us to the third item. An Inexpensive Voltage Controller Heckel, McAllister, and Lunney published plans for a voltage controller based on an inexpensive household dimmer switch (3). In 1971the cost was under ten dollars. Ten years later we were able t o n m s t r t ~ thesnme s~ device rser Fig. 31 iur rourhlv rhe idmtiwl rox. This was umsible berausc th(.rt,it of the-dimmer switch has not increased its price over the years.

Figure 1.

A light bulb hot plate (modified from that of L. C. Kreider)

Figure 2. Three "homemade" heating devices. The light bulb hot plate (left). voltage controller (center) and electric flask heater (right).



Journal of Chemical Education

Figure 3.

Circuit diagram tor voltage controller (reproduced from reference


Acknowledgments I would like to thank Gerry Cohen (age 13) for the construction of the light bulb hot plate and electric flask heater, and William (age 15) and Alexander Cohen (age 17) for the building of the voltage controllers. The construction times given in this colulnn are those of the teenage builders. Literature Cited (1) Kreider, L.C., J. CHEM. EDUC.,12,336 (18351. (2) Mathews, F.. J. CHFM. EDUC.,28,258 (19511. (3) Heekel, E., McAllister, W. A,, and Lunney, D.,J.CHEM.EDUC.. 48,586 (19711.