What Makes Mercury Special , So That It Can Be Used In A Thermometer?

One thing it does darn well, is adhere to gold. Miners have used liquid mercury since ancient Egypt. It's primary use was in separating fine gold from the black sand (which is quite heavy itself, and very hard to separate from gold of similar size...as in "flour gold"). The compound derived from adding mercury to gold is called Amalgam. It is off-white in color and if you were to place a "glob" of amalgam in a gold pan with clean flour gold, it will quickly bind itself with the mercury/amalgam and all turn the off-white color.  Mercury in the liquid state is not dangerous, as long as common sense is observed....along with a little knowledge. As long as you dont get it into an open wound or into your eyes/nose/mouth, you are totally fine handling it. What caused the death of miner's who used it then? Well; In order to separate the mercury from the gold, once you separate the gold from the other minerals,  you have to burn off the mercury. Miner death resulted from the brain damage caused by inhalation of the mercury fumes when burning it off of the gold.That is the dangerous state of mercury....or rather the deadliest by far.

    If this is supposed to be a medical question, I have no clue what medical uses there are for "quicksilver".......