PLUS OR MINUS?

Radio Record, Volume I, Issue 4, 12 August 1927, Page 14

PLUS OR MINUS?

TO ASCERTAIN WHICH IS WHICH.

Difficulty in ascertaining which is a positive or negative wire connected to a battery is frequently experienced by radio fans. This applies particularly to loudspeaker cords. Connecting the loudepeaker with the wrong polarity causes weakening of the magnet within it. The simplest method of testing the polarity of wires leading from storage hatteries of small voltage is by grasping any pipe or ground wire with one hand and touching the wire you desire to test to your tongue. ‘The positive wire will give you a slight sensation or a sort of sour taste; the negative will have no effect Do not attempt this, however, with alternating current, or, in fact, any current of, high voltage. With any voltage up to 110, you can determine the polarity by touching with a fingertip. If an alternating current, touch very quickly If it is a positive wire vou will get a slight shock; if negative, there will be no effect. Direct current (used in radio receivers) will cause a slight tangling feeling, whereas alternatine current will produce a shock. There is no daneer in making these tests on ordinary batterv power in connection with radio. If, lhowever, vou prefer a different means, place a little common salt in a elass of water and insert the ends of both wires in the solution. ‘There will be a bubbling around the nevative wire, while the positive will apparently produce no effect on the water.