Increased Utilization of Electronic Apparatus A number of student laboratory experiments use some electronic apparatus in conjunction with a sensing device or probe. Common combinations include the "resistance bridgeN with simple electrodes or a thermistor, and the pH meter/glass electrode. I n a number of applications, such as when the progress of a reaction is monitored, the probe remains in the reacting system throughout the experiment, although readings are only taken every few minutes. I t is possible to utilize more fully the main instrument by connecting it t o several probes via a simple switch unit-the selected probe can then be connected directly to the instrument when required. I n this way one instrument can be used to monitor several separate reactions. We have used easily made, inexpensive (components cost about $12) switch units with conductance bridges in student kinetics experiments with complete success. Four double pole press-on type switches (only one can be on) connect the input lead from the bridge t o a selected pair of output terminals. T h e switches and four pairs of output terminals are mounted in a small aluminium case. Platinum electrode assemblies, in four separate thermostatted reaction vessels are each connected t o a pair of terminals on the switch unit. When required, the conductance of a given solution is measured with the bridge after pressing the appropriate switch. No adverse capacitance or screening effects were encountered when operating a t 60 Ha or 1000 Hz. There is no reason why similar units, with appropriate leads and terminals, could not be used with 8. variety of instruments. V. TWIGG ERINDALE COLLEGE MARTVN OF TORONTO UNIVERSITY TORONTO 181, CANADA
Volume 49, Number 3, March 1972
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