[princeps mundi]

I used two copper electrodes in a solution of KNO3, and ran something on the order of 100 mA through it.  For a while, a gas bubbled off at one electrode (I don't know the polarity so let's call it A).  On the other electrode (B) a bluish solid formed.  I believe that the gas is H2 and the solid is Cu(OH)2, as I wanted.  However, after a few minutes, a black solid started forming on the B electrode.  I removed the sludge, and it does not appear to be soluble in acedic acid.

The question is, what is the black solid?

I was fairly careful and had cleaned out my beaker and used distilled water, etc. and there was a lot of the black solid, so I don't think it can be attributed to contamination.

[Borek]

Please search forums for woelen posts, I am sure he discussed similar experiment in details some time ago. I hope it was on chemicalforums, not some other place