LN2
I use the stuff on a weeky basis and I can tell you this... It stings... when it eveporates it leaves a small white patch of (frozen skin? condensed water...) or something... I have gotten some splashed on my shoe once... I just scrunched up my toes to the other side of the shoe and was fine
But yea that is how we know the dewar is full when it all comes splashing out the top... It is alot like fire... you can put your finger through the flame for only so long....
Tokamac