What will happen on touching mercury?

Mercury can be absorbed transdermally -- through the skin. Over time it accumulates in the system and causes heavy metal poisoning (as does, for instance, lead). Symptoms include dementia, vomiting, uremia, cramping, oral and pharyngeal pain, diarrhea and death. One touch will not kill you, or necessarily even cause symptoms but, like all heavy metal poisoning, it accumulates in your system. A side note: the term "mad as a hatter" probably came from hatmaker's use of mercury to cure the felt they used to make hats, which caused dementia.