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Which one is the positive?

Discussion in 'Electronic Basics' started by Joe McElvenney, Dec 22, 2004.

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  1. Hi,

    There is a question a little way up the group about a power
    connector and which of the leads is positive/negative. Now
    supposing you had the same problem with only the contents of the
    average kitchen cupboard to hand, how would one go about
    determining polarity?

    I seem to remember from my school science classes of many
    years ago, such things as gases bubbling off the end of wires
    immersed in slightly acid solutions (vinegar and water) or maybe
    electro-what's-it (as used in DNA matching) employing possibly
    toilet paper and some easily to hand substance.

    Any ideas ??

    Cheers - Joe
  2. I hear you but there are so many 'cheapo' digital meters around now that
    IMHO everyone should have one in the cupboard, much easier than making
    solutions and handy for lots of situations.
  3. John Fields

    John Fields Guest


    Yes; it helps to find them! ;)
  5. John Fields

    John Fields Guest

    John Popelish's link was good, but I didn't see any way to determine
    whether the positive or negative wire was evolving hydrogen. Try

    1. Get a large, electrically non-conductive container (Teflon coated
    pot, ceramic casserole dish, or something like that) and fill it
    with tap water.

    2. Submerge two small glasses in the pot so that they fill up with
    water, then turn them over underwater so that their rims are
    touching the bottom of the container and they're still full of

    3. Get two pieces of wire long enough to reach from the bottom of the
    pot to your power supply connector.

    4. Strip one end of both wires and slip the stripped ends under the
    rims of the glasses without letting any air get into the glasses.
    One wire per glass, and make sure the stripped ends don't stick out
    from under the glasses.

    5. Strip the other ends and connect them to your power supply.
    Gas bubbles should begin forming on the stripped ends of the wires
    under the glasses.

    6. Let everything keep going until enough gas has collected in the
    glasses so that you can clearly see that one glass has twice as
    much gas in it as the other. The wire under that glass (the one
    with twice as moch gas in it) will be connected to the negative
    terminal of your power supply.
  6. The positive electrode will release oxygen an the negative will
    release hydrogen. There will be twice as much hydrogen as oxygen.
    More bubbles = negative.
  7. John Fields

    John Fields Guest

  8. I think it is implied because 2*H2O becomes 2*H2 and 1*O2. H20 has
    twice as many hydrogen atoms as oxygen atoms. Split it and you get
    twice as much hydrogen as oxygen.
  9. But in the not-so-real world of a homework problem, they don't have DMMs
    in the cupboard. ;-)
  10. Guest

    Dumb question time. If you ran AC for the electrolysis, would you get
    separated H and O in each glass? (one gas on each half cycle) Could be

  11. You get mixed H2 and O2.
    Very! Google [brown's gas].
  12. It's possible that whatever gas gets formed during one half cycle is
    reabsorbed during the other half cycle. But that's just a WAG.

    Just take the gas separation stuff - inverted test tubes or whatever -
    off and let the gasses mix together in the same glass. That way, you
    can use DC.
  13. Robert

    Robert Guest

    What a rat's nest. The first link after googling on "brown's gas"


  14. Yea. Isn't it amazing that electrically breaking water into its
    component elements can make so many people lose their minds?
  15. Charles Jean

    Charles Jean Guest


    Back to the original post, here's an old chemist trick that works:
    Dissolve salt in distilled water to make about a 5% solution. Take
    about 1/2 cup of the solution and add 10 drops of phenolphthalein pH
    indicator solution to it. Mix well and place it in an inert container
    plastic or glass-the plastic 1/2 cup measuring cup works well. Clip a
    couple of connectors(the insulated wire/alligator clip on both ends
    type) to opposite ends of rim of the measuring cup. If needed raise
    the level of liquid in the cup until its brim full-both alligator
    clips must be touching the liquid. Now connect the other ends of the
    connectors to the voltage source. Let stand undisturbed while
    electrolysis produces a red-purple stain in the solution surrounding
    one of the electrodes. That's the negative electrode. As the
    electrolysis proceeds, the pH around the negative goes up, while the
    pH around the positive electrode goes down. Whenever the pH reaches
    about 8.3 it changes color from colorless to purple.
  16. Robert

    Robert Guest

    I can't understand the claim of producing monatomic H and storing it. I
    thought that it would combine to diatomic H2 at room temperature on it's

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