So you don't know which is bleach and which is fix?

An easy way to test this would be to take a piece of developed B&W film leader (so that it's completely black), dip it in one of the solutions for a minute or two. If it's the bleach, you will be able to see it start to bleach back the submerged area of the leader. In order to avoid cross contamination, you don't want to use the same strip of leader for both solutions.

My money is on it being the darker solution.

Jason