Shine a light into the can and see if the inside of the can is rusty. The old IMR cans are suseptible to rusting inside and leave a brownish dust on the powder. Also, pour the powder into a large receptical and see if brown "dust" rises off the powder as you pour it. If the powder SMELLS like either or a solvent and is not pungent or acidic smelling, it probably is OK. I have shot powder like I described and have not had problems. If there is ANY doubt, it makes great fertilizer on your roses.