"Mike Henry" wrote in message
...
snip-----

I'm not a chemist either, but I wonder if H+ is the worker here. If it
was
, it seems to me that sulfuric acid would work as well as nitric and
that's
apparently not the case. Nitrate (NO3-) is known as a good oxidizer, so
I'm
thinking that it is the active component in nitric acid, perhaps oxidising
the iron in steel to Fe(NO3)2 or some other form. Googling the subject
has
not been productive for me, but a post to sci.chem would probably turn up
the correct reaction. Once that is known it should be a simple matter to
calculate how much nitric acid would be needed to dissolve the screw or
tap,
as the case may be.

BTW, somewhere in the results of a Google search it was suggested that
concentrated nitric acid be diluted before application.

Assuming reaction to Fe(NO3)2, you'd have:

2 HNO3 + Fe = Fe(NO3)2 + H2

so you'd need 2 moles of ntric (126 grams) for every mole of iron (55.8
grams) in the tap, or roughly 2-1/4 gram of pure nitric per gram of iron.
For a 70% nitric acid solution that would be a litlle over 3 grams nitric
per gram of iron and a 1:1 dilution of nitric acid would require around 6
grams nitric acid per gram of iron. The approach is correct, I think, but
the reaction could be all wrong. Note that hydrogen is released in the
above reaction. If the solution bubbles, some sort of gas is being
released
and hydrogen is probably more likely than oxygen.

Mike

While I can't confirm what you said, Mike, I recall that on rare occasions
I'd have a minor hydrogen fire------which indicates to me that you are on
the right track. If the hydrogen was being consumed, there'd be nothing to
burn. It's obvious it is liberated, with the metal in question taking its
place.

Harold