Answer:
I can travel from there to here by disappearing, and here to there by reappearing.
Feed me and I live, give me drink and I die.
What can you put in a barrel to make it lighter?
What I am filled, I can point the way. When I am empty. Nothing moves me. I have two skins. One without and one within.
What is the only letter in the alphabet that does not appear anywhere on the periodic table of elements?
My days are numbered. What am I?