Grant Erwin wrote:

I got a little bit of 70% nitric acid, potent stuff. I cut the end off a
screw of the same exact type as I previously dissolved in alum, put it
in the bottom of a small glass, and added about 10 drops of nitric acid.
Naturally, I wore face shield and gloves, and used an exhaust fan.
Nitric is pretty nasty. Anyway, it was cooking along nicely for a few
minutes but then it seems to have slowed down quite a bit. It's been
going about 8 hours now, and I'm wondering if there is enough oomph in
the little bit of acid I put on it, barely enough to cover the bottom of
a small water glass.

Thing is, my actual screw, which is in an aluminum casting, won't have
much acid around it either.

I suppose I could try drawing the liquor out carefully after it slows,
and adding a few more drops.

Anyway, tomorrow I'll take the piece out and weigh it and I'll get a
rate of dissolution and then I'll compare it to how the alum did.

GWE

You do consume the acid as it dissolves the metal. You'll bubble off
hydrogen while the iron is being oxidized, ultimately you'll have a
solution of ferrous (ferric? ick) nitrate (or whatever) and no acid.

I suspect that if you just drip more acid around the screw you'll get it
down to where it needs to do its work -- but you'll also have some
dripping out of the hole, which may not be what you want.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com