Polarity Indicator
   From the 1929 catalogue of the Chicago Apparatus Company: Polarity Indictor. Consists of two electrodes sealed into a glass tube filled with a chemical solution. When connected into a circuit the solution about the positive electrode turns red while that about the negative remains uncolored. Useful in determining the polarity of circuit terminals and the direction of current flow. For use on D.C. circuits up to 30 volts $2.25; for use on D.C. circuits from 50 to 600 volts .. $3.00. This device is in the Greenslade Collection
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