The battery contains Sulfuric acid and this can burn the skin. The best treatment is to wash the effected part in cold water, much the same as any type of burn.
If you mean like AA or AAA, nothing. Absolutely nothing happens. If they both have an electrical current running, I don't know, it might be dangerous.
Dead battery -will no longer charge.
changes color
It changes color.
Tordon is a herbicide and when it comes in contact with skin, the skin will become irritated.
It changes color
Contact Metamorphism: When magma comes in contact with other rocks it will heat them and change them into new rocks. This often happens around an igneous intrusion.
it change color
It changes color
It'll turn purple.
It changes color.
It is very corrosive and will cause any metal it comes in contact with to rust.