Simple Polarity Test

Radio Record, Volume III, Issue 9, 13 September 1929, Page 29

Simple Polarity Test

USY amateurs on the look-out for a rough-and-ready, but nevertheless satisfactory test for determining the polarity of their batteries, cannot do ‘better than employ the following method, which although, of course, not being as sensitive as the more refined chemical tests, works quite well on potentials of over four volts. The test is simplicity itself. Take. an ordinary potato and cut a slice from it. Apply to the surface of the slice the battery electrodes, keeping them about half an inch apart. After about ten seconds’ contact with the freshlycut potato surface the positive electrode will give rise to a dull-green mark, the area of contact of the negative electrode remaining unstained. A freshly-cut onion gives somewhat similar results, the stain, however, at the positive pole, in this case, being brownish. The onion test, however, is rather less sensitive than the potato, test, requiring higher voltages in order to give results.