Believe it or not Mercury is not just a planet in the solar system, but a metal that is very hard to dispose of. Mercury used to be used in almost all thermometers, but now is very difficult to get rid of. Very few (if any) scrap yards want to buy Mercury, so that puts a lot of people in a bit of a predicament when they come across it.
Mercury can be looked at to be very toxic if handled in the wrong way, and because of that you want to make sure to have it recycled in the right place. Most (if not all) scrap yards will not buy or even take Mercury for free, and that leaves you in a tough circumstance.
One tip is to contact your town and find out where they would recommend getting rid of Mercury correctly and in an environmentally friendly way. There are still some current uses for Mercury, but most are in scientific uses now.
Mercury is also used (but rarely) in tooth fillings as well as in certain capacitors for electrical systems.