You find an unused can of Zyklon B what do you do with it?

Call the fire dept. they will know how to dispose of it. My uncle called them one time after he found a bottle of gun blueing in his cabinet that he forgot about. They showed on the news that it gets unstable and becomes as volatile as nitro-glycerin when it gets old enough. The fire department send firefighters to collect it and told him he did the right thing.