Do you have any pipettes? Take a few drops worth of the liquid and see if they mix with water. If they don't, it would make sense that this is a sample of a reactive metal. Next, without taking it out of the liquid, scrape the surface with something and see if it is silvery under the white layer. If it is, you are probably looking at one of the following: sodium, potassium, calcium. It doesn't float in the liquid right? That would possibly mean it is lithium if it did. If it does seem to be a metal, I would buy some mineral oil (look at the laxative or maybe baby care section of your local stores) and replace the liquid in the container with it.