Mercury is a metallic element. You can't "dispose" of it because you can't destroy elements.
Mercury at room temperature in a glass container is not dangerous. If the top is "leaking" then some simple disposable gloves would be a wise precaution. Most metals are poisonous to humans when concentrated in the body.
Mercury isn't the most dangerous metal but it's probably the most feared by the public. Other metals like Lead, Arsenic and Uranium are much more dangerous in smaller quantities than Mercury.
The key to handling dangerous metals is to prevent build up of the metal in your body tissues. With Mercury that's best accomplished by not breathing the fumes. Mercury vaporizes very slowly at room temperature. That's why mercury is stored in glass with a layer of water on top to prevent any mercury vapor from escaping. I'm guessing that's why Capt. E. thought the mercury he found in a glass jar was leaking - because of the water in the jar.
Pure metallic Mercury, when stored correctly, really isn't dangerous to humans. If you like science you can watch this video of scientists explaining how little health danger metallic Mercury has while submerging their body parts in liquid room temperature Mercury.
Where Mercury gets it's bad reputation is from when little bacteria process the metallic mercury into methylmercury an organic (carbon) compound. Methylmercury is really dangerous to human health. The creation of methylmercury from native mercury is a natural ongoing process that has nothing to do with mining or human activity. It's found in waterways wherever there are natural Mercury deposits.
You encounter Mercury every day as you go about your life. Besides the obvious mercury florescent light bulbs now being used everywhere to save the environment Mercury is also found in your water pipes (PVC contains mercury) many pigments in paints, cosmetics and plastics, explosives and many medicines. I doubt there is any way you could ever stop being exposed to mercury.
That little jar of Mercury has some real value. It likely has some gold amalgam as well as the value of the Mercury itself.
Mercury sells for about a dollar a gram. Many people will tell you it's been banned but the only restriction on Mercury is that it can't be transported by air.
If you were to call your local authorities to alert them to the presence of this natural metal they would ultimately, after all the drama and paperwork, process and recover the Mercury in the same way the miner who buried the jar would. They would use a retort to recover the mercury and gold and sell them into the market. It is after all is said and done a useful natural element that's a lot less dangerous to humanity than automobiles or chain saws or the flu.
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