# Which one is the positive?

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

1. ### Joe McElvenneyGuest

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. ### Rheilly PhoullGuest

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 FieldsGuest

....

Yes; it helps to find them!

4. ### John PopelishGuest

http://www.nmsea.org/Curriculum/7_12/electrolysis/electrolysis.htm

5. ### John FieldsGuest

---
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
this:

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
water.

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

6. ### John PopelishGuest

The positive electrode will release oxygen an the negative will
release hydrogen. There will be twice as much hydrogen as oxygen.
More bubbles = negative.

8. ### John PopelishGuest

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. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

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
'explosive'.
GG

11. ### John PopelishGuest

You get mixed H2 and O2.

12. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

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. ### RobertGuest

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

http://www.phact.org/e/bgas.htm

Robert

14. ### John PopelishGuest

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

15. ### Charles JeanGuest

___

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. ### RobertGuest

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
own.

Robert