"Tom Miller" wrote in message
...
If I remember correctly, cast iron is more resistant than steel, to attack
by sulphuric acid. If you can fill the hole with H2SO4, you may find that
it
dissolves enough of the drill to remove it. You'll have to keep trying it
on
a regular basis though, as I have no idea as to how long it will take. I
could give you the usually boring warnings about strong acids and gloves
and
glasses, but if you don't know enough about already, you shouldn't mess
with
it at all.

Tom miller

Truth is, iron won't dissolve in *concentrated* sulfuric acid, but if
there's any water present, all bets are off.

Cast iron kettles used to be used in processing sludge from silver cells, to
separate residual silver particles from the sludge, from which the rest of
the precious metals were extracted (gold and the platinum group metals).
The silver particles were dissolved by boiling the sludge in concentrated
sulfuric acid.

Harold