Almost 2 years ago I closed the pool at our old house for the winter. I took a box of white powder and dumped it into an old coffee can for storage. I very cleverly did not label the can. Then we sold the house the following February. Fast forward to this summer when I finally get the pool up at the new house, I've got a coffee can of something. I think it's borax, it doesn't appear fine enough to be baking soda. Is there a way to test for sure?