Again, I'd ask that you not dispose of it yourself. Contact a chemistry department near you and see if they can put it into their disposal process. Speaking as someone who sees such things now and then at my school, I really wouldn't mind if somebody dropped it off anonymously for professional disposal. I'd rather have that than have it wind up in some landfill. Likewise batteries. Most schools have procedures in place to deal with such things.
Mercury is one of the very most serious environmental concerns, and the reasons for that are only just now becoming more clear. The organic compounds of mercury are especially hazardous; the pure metal form isn't so bad but can become equally hazardous if stored improperly or reacted with various other things. Generally the mercury compounds are one of very few things that can easily cross the blood brain barrier and remain fixed (perhaps un-chelatably fixed), which gives rise to all manner of speculation and ongoing research regarding role(s) in mental illness. Various forms also can pass through plastics very easily- and at least one expert chemist perished while researching this very point. She got an invisible quantity absorbed via a glove, which wasn't even torn. That was dimethyl mercury, IIRC, one of the very worst chemicals you can come into contact with.
While I respect the goals of some to do daguerreotypes and such, 99.44% of us have no business having this stuff on our shelves. I am really not even sure that I respect the right of any individual to have it on their shelf. I have all manner of potions in my lab and in even in that case I try to keep the very highest levels of safety; I'd certainly not keep it or chromium intensifier etc. in a home darkroom. I also am not so sure it's a good idea to pass the stuff on to some enthusiast who may or may not handle it properly. The more mercury we can put out of commission, the better. We shouldn't pass it on as a favour or try to keep the price low by trading it around... the price on it should be very high because disposal is very very difficult. It's bad enough that all the enviro-idiots without degrees are telling us to fill our homes with CFLs before there is any legislation to deal with the mercury waste. Let's not contribute even more to the environment.
When Jack Mitchell died, I had the task of going through his darkroom. Boy oh boy did Jack have some items! Glowing items. All manner of the nastiest photographic potions imaginable- and most of them completely untouched in many decades. Took our enviro folks quite a long while to get it all out. But they did handle it all safely and professionally. Really folks, let the pros do their thing, it's what they do.
