"electrolysis"

Alan, I would suggest that you consult a recognized text on physical chemistry were topics like yours are addressed to an ad nasium extent. Glasstone and Lewis' "Elements of Physical Chemistry" (Van Nostrand) provides a reasonably good explanation and analysis.

I belive that the point that you may be missing is that there is a fuzzy but definite distinction between electrolysis and the electroplating process, and while I am no means an authority on the subject, I believe it has to do with the reactive nor non reactive nature of the electrodes emplyed, the electrolyte itself, current density and a number of other factors.

For electrolysis, platinum, platnimized titatium and several other relatively non-reactive electrodes are employed. Were copper to be employed as an electrode, the copper molecles (or atoms) are easily disassociated into ions that are imparted with a migration rate dependet on the electric field present in the electrolyte, creating not an electrolysis cell, but a copper electroplating system. I believe what the blue coloration you see during your test is that while migrating to the cathode, the copper ions have chemically interacted with other ions present in the electrolyte creating copper oxides, copper sufides, and other compounds which then remain in solution or precipitate out after formation.

I've never built an electrolysis appartus per se, but have done a considerable amount of electroplating in the printed circuit board industry. For plating copper, nickel, silver or solder, we employ anodes made out of these materials, which decrease in mass with use. For precious metal plating we emply electrodes of precious metals such as platimized titanium, and the ions that we deposit on the destination are supplied by the precious metals that we purchase already in solution including gold, platinum, and rhodium. That way, the electrodes take no part in the electrochemistry.

I would tend to assume that for electrolysis, you would want to emply a similar non-reactive electrode, and at least an anode consisting of such an element.

An electro-chemist or a physical chemist could tell you more, but then neither is my specialty as a scientist.

Harry C.

Allan Adler wrote:

p.s., Allan, are you still associated with the Media Lab. Interesting things I've been seeing coming out of that fun place lately. Is Minsky still running the show?

Harry C.

Allan Adler wrote:

Thanks.

I was aware that what I was describing was not electrolysis. That's why I put it in quotes in the subject line. However, if I did want to dissociate water, for example, I would use a very similar set up. I've done so in the past and it is also something I'm considering. More on that another time.

The main thing I'm concerned about is safety and I'm not going to find out about that from a physical chemistry book. My question was how likely I would be to get electrocuted from using a typical AC adaptor instead of batteries. More precisely, what additional precautions are necessary when upgrading from batteries to AC adaptors?

To answer the question you asked in your other reply, I have NEVER been associated with the media lab.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

Allan, you posted:

"The main thing I'm concerned about is safety and I'm not going to find

out about that from a physical chemistry book. My question was how likely I would be to get electrocuted from using a typical AC adaptor instead of batteries. More precisely, what additional precautions are necessary when upgrading from batteries to AC adaptors?"

Allan, the primary precaution to take in avoiding electrocution in working with AC adpapters (at 115-Volts) is to be certain that your body does not provide a current path to ground at any time. This means to insulate yourself from ground by not working when standing on a wet floor in bare feet or conductive shoes. Many of us work on a bench with a a high resistance rubber mat (to dissipate static electricity) under out feet, and wear a ground strap on our arm connected to ground with a

500-K or greater value current limiting resistor to prevent static buildup, but are otherwise insulated from ground. This is done to prevent damage to ESD sensitive semiconductor devices only.

What you do not want to do is to work with 115V or higher voltage circuitry when directly grounded.

Voltages under 10 or 20 Volts usually present no danger, unless through access to the internal body fluids as with some medical instrumentation procedures or electrode contact through a deep cut or other opening in the skin.

Hope this helps, Harry C.

Allan Adler wrote:

Batteries to AC adapters seems (to me) to imply some reduced transformer voltage like a "wall wart" power supply. They are isolated from the 120 VAC and ground so present little risk of electrocution (providing the wall wart remains dry).

Wall warts are also current limited to one extent or another - although in some cases that just means that they burn out before they catch fire.

If you are comtemplating using high voltage mains power, an isolation transformer is a good idea. AND OR a Ground Fault Interrupter. You can get GFI extension cords these days if you can't simply install a GFI receptical by your set up. They work! (as I discovered in a hotel when the coffee maker overflowed and I grabbed the pot - you feel the tingle but it won't knock you down)

If I were fooling with that stuff, and for some reason wanted to us AC in the electrolyte, I'd use an isolation transformer with a voltmeter, ammeter, and variable transformer to control it.

You can get shocked with less than 12 volts under some circumstances, especially while putting one's hands into current carrying electrolytes. Stay safe and avoid using two hands at the same time (after you've isolated the voltage from ground). Broken skin, and 12 volts can get your attention.

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Thanks for this and other suggestions, and to others who offered advice.

I am only thinking of AC at the moment. However, I can imagine some reasons down the road why I might want to use AC in the electrolyte, so this is good to know.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

I do something a bit similar with washing soda, to de-rust old ironwork, google will tell you more about this technique.

For power, I use an old PC power supply from a dumpster PC, and to limit the current, I put an old car headlamp in series (you can use a 'blown' headlamp as long as one filament is still good) (put the lamp on a non-flamable support)

Generally I use the 12V 8 Amp output for the electrolytic experiments, but you might need to put another lamp on the 5V output to keep the power supply happy since they sometimes won't run without a load on the 5V wires.

Make sure you can't get water into the power supply, and of course be careful not to touch the AC power wires when your hands are wet.

Chris

Thanks for the explanation. Now I have another reason to fish old PC's out of dumpsters.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.