A Modified Water Rheostat Ping-Yuan Y e h and Chen-Pin Y u National Taiwan University, Taiwan, Chino
A modified water rheostat apparatus, as shown in the figure, may be easily constructed from two pieces of glass tubing (2 X 50 cm and 3.5 X 40 cm) and copper wire electrodes (3 mm diameter). Variable voltage is obtained at the heater, stirrer, etc., by chancine the distance between the two electrodes. The upper movable electrode is covered and insulated by a small piece of glass tubing. Spiral wire electrodes are recommended in order to lessen coverage of the electrode surface by the precipitates formed during the electrolysis. Using a 750-watt heater, a 20% sodium chloride solution, and an input voltage of 100 volts, variable voltages between 15 and 75 volts were obtained. Similar voltages were obtained from a 300-watt heater and a 4% sodium chloride solution. Advantages of this modified water rheostat include its small size, inexpensiveness, lack of splashing, low rate of evaporation of the salt solut,ion (less than 1 ml/l hr), constant t,em~eratureof the salt solution durine operation, and an essentially constant water voltage obtained at the heater or rheo.tot. I ~ O O I . stirrer. A large Liebig condenser may iw water; B, NaCI he used in place of the two pieces of glass tubing. or stirrer, etc.
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:zey R,E'h:2:;
Volume 36, Number 9, September 1959
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473
