Back before Webster_1913 started noding, I had entered a short writeup here, drawn from my career experience with a battery manufacturer:

   "An electrode with a negative charge. The "minus" end of a battery. Compare with Cathode."

...and all was well. After Webby's spree, it was not until Sun Nov 25, 2001 (yup, two years) that some_guy was kind enough to /msg me about the contradiction. It's been a while since last I ran a surface resistivity test on a sample of anode film, fresh off coating line #8. However, I like to think I at least knew my stuff when I actually wrote it... So I turned to to back me up. Here's what they had to say (my emphasis in boldface):

   1. A positively charged electrode, as of an electrolytic cell, storage battery, or electron tube.
   2. The negatively charged terminal of a primary cell or of a storage battery that is supplying current."

Whoah. So is "anode" positive or negative? The conflict lies in the counterintuitive designations of "positive" and "negative" in electronics. By way of explanation, let's take a little trip down public education memory lane... In junior high General Science, we learned that atoms are composed of neutrons, positively-charged protons, and negatively-charged electrons. Those of you who paid attention (and you know who you are) will recall that the electrons whirl around the ouside of the atom like a swarm of killer bees, while the protons and neutrons snuggle down in the center (or "nucleus"... oh, that wacky scientist jive talk!) of the atom. In dense metals, like copper, lead, and gold, the electrons exchange relatively freely between atoms. So freely, in fact, that you can use metal to carry a "current" of electrons, clear from one end of a metal wire to the other. It's almost like pushing a water current through a pipe.

That's a very useful analogy, actually. Pressure forces water through the pipe, squeezing it at the high-pressure side so that it travels to the low-pressure side, where it has more room to expand. Likewise, a concentration of negatively-charged electrons exerts a kind of pressure; scientists and other jargon snobs call this pressure "potential". Electrical current, then, is said to travel from a point of high potential to a point of low potential.

Here's the tricky part: the point of high potential is said to be "positive", even though that high potential can be envisioned as negatively-charged electrons under pressure! Hence the confusion. (And hence my mediocre performance in the second half of high-school Physics.) So, in chemistry-speak, the anode is indeed "negatively charged" (q.v. anion); it has the higher concentration of negatively charged electrons. In electronics-speak, though, the anode is positively charged; it has the higher electrical potential.

An important fact about anodes and cathodes is that chemical processes will occur when they are submerged. For example, electrolysis occurs when electrodes are dropped into salty water. (The water has to be salty so that it will conduct electricity.) The chemical process created causes oxygen to be released from one electrode, and hydrogen from the other.

The process at the anode is called oxidation, and the process that occurs at the cathode is reduction. A good nmemonic for the whole thing is the sentence, "An ox and a red cat".

This finds practical application in many areas, and one known to most people (whether they know it or not) involves the "zincs" on a boat. They are pieces of sacrifical metal performing as the anode in cathodic protection, creating a beneifical electrical field to keep the propellers from corroding away.

An"ode (#), n. [Gr. up + way.] Elec.

The positive pole of an electric battery, or more strictly the electrode by which the current enters the electrolyte on its way to the other pole; -- opposed to cathode.


© Webster 1913.

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