>Well, I never said you used the wrong stuff.  I just said that iron
>oxide is rust.  Phosphoric
>acid actually works by removing the iron oxide (rust).

In fact it doesn't remove the rust, it alters it chemically to a
pretty-much insoluble & inert iron compound, but I'm not sure which.
Possibly iron sulfide (of which one form, marcasite, is chemically
active, and the other, iron pyrite, is not).