I know this is dumb, and I probably know the answer, but here it goes:
I keep my fresh film in the plastic cases they come with (pill box looking plastic cases) on one side of my desk, and on the other I keep my used film in the same sort of cases. While my house keeper was cleaning up she mixed up the both sides into one neat little pile, how do I tell them apprt?
theres no way of telling by looking at the rolls. Both have a little bit of film sticking out so visually they are all identical.
These photos are valuable to me and I need them to make my self money
Is this a live and learn experience or is there something i could do, other than develop 40 rolls of film
Perhaps I'll rephrase your question to, "is there something i could do, that's cheaper than developing those 40 rolls of film?"
There is probably no way to visually see which ones are exposed or not, unless the length of the tab is amazingly consistent, and different between used/unused.
When you load the film in the camera though, you pull the film out about three inches. This bit of film immediately becomes completely exposed. You could pull about two inches off each roll and develop them. That will show which ones are unused, and which have been used.
Before doing this, check that whoever develops your film can do so, with film that's cut to a square end since the tab is now gone. And you may need to cut a rough tab onto the unused rolls to load them (they're now 22 frame rolls...)
It's only really worthwhile doing all this if those unused rolls are really precious!