Morothon Oil Co. Littleton, Colorado 80121
Exothermic reactions usually are controlled in the laboratory by adjusting the addition rate of one of the reagents or by manually cooling the reaction flask with an ice bath. The use of an automatic device, the Jack-O-Matic, that raises and lowers an ice bath as the flask temperature demands has been described.' This versatile device suffers from one disadvantage: the Jack-O-Matic is powered by compressed air. Compressed air sources are usually not as readily available in the laboratory as are electrical outlets. All-electric power jacks are more convenient, and most have a remote control switch that can be unplugged when desired.
A'
HIGH LIMIT O
swmcn
Diogrorn of outornotie temperature control.
We have replaced such a remote control switch by two normally closed leaf switches that can be easily positioned on a ring stand to limit the upper and lower positions of the power jack. These limit switches are used with a Therm-O-Watch2 so that an ice bath is raised whenever the reaction flask temperature gets too high, 422 / journal of Chemical Education
as judged by the Therm-O-Watch and is lowered whenever the flask is too cool. The accompanying schematic diagram illustrates the wiring. Dotted lines enclose the partial wiring diagrams of the Therm-O-Watch and the power jack.a I n this operation, the power jack derivesits power from the Therm-O-Watch rather than its own line cord. Thus a shorted line cord socket must be plugged onto the power jack line cord plug in order to complete the circuit. A standard Cinch-Jones three connector plug is used to connect the leaf switches to the power jack remote control outlet. Two grounded ac line plugs connect the wiring to the Therm-O-Watch. The schematic diagram shows a too cool situation. The power jack has just lowered the ice bath until the jack platform encountered the low limit switch. This encounter opened the normally closed switch and the jack stopped. As the reaction flasks warms, either naturally, or from a heater such as an infrared lamp plugged into the optional heater socket, the Therm-OWatch senses when the set temperature is exceeded, and the relay switch changes from the position shown in the diagram. This action now supplies line voltage to contacts 1 and 2 of the Cinch-Jones plug, and the jack lifts until the platform encounters the high limit switch, which opens the circuit, stopping the jack. When the lifting starts, the previously open low limit switch reverts to its normally closed position. The ice bath will remain in position, cooling the reaction flask until the Therm-O-Watch senses the cooling and its relay switch switches back to the position shown. This supplies power to contacts 2 and 3 of the Cinch-Jones plug until the jack platform lowers and encounters the low limit switch, opening it and stopping the action. This completes the cycle, and all switches will again be as shown in the diagram. This situation showed plugs A and B inserted into sockets C and D, respectively. By changing this so that plugs A and B are inserted into D and C , respectively, the jack will raise when the reactor is too cool, and lower when too hot. Thus for a reaction that requires heating rather than cooling, a hot oil bath can be substituted for the ice bath, thus heating the reaction flask as needed. Care should be taken to insure proper grounding as shown in the schematic, and to use adequately insulated wire and switches. COLON, D. R., J. CHEM.EDUC., 43, A737 (1966). Therm-O-Watch Controller, Model L6. Instruments for Research & Industry, Cheltenhsm, Pa. 19012. Precision Scientific Co., 3737 W. Cortland St., Chicago 47, 111. 1
