In one sense the whole scientific approach is about proving yourself wrong, which could be seen as making "mistakes"

Penicillin is a famous one.

I think you're talking about a different type of mistake than nitrogen is. You seem to be talking about accidental discoveries, or discoveries that were discovered while using mistaken techniques.

When Alexander Fleming discovered that penicillin fought bacteria, he was not mistaken at all. He was spot on- it did kill bacteria. Sure, its discovery may have been caused by a mistake, but what he learned about penicillin was correct, as far as I know.

Ah yes sorry I isolated the point up to cup's comment.

But I'm still sure that there are/will be times when great discoveries are proven to be mistakes. Barring practical ones like penicillin, there has been numerous 'discoveries' proven wrong much later; Newton's colour theory comes to mind, and of course the rather famous its-a-particle-no-a-wave ping pong.