Critical temperature for liquid nitrogen is

Critical temperature (Tc) of substance is the temperature at and above which vapor of that substance cannot be liquefied, no matter how much pressure is applied (Note: Below critical temperature a substance can exist as a liquid or gas depending on pressure).Critical temperature of N2 is-146.9degC; that means N2 can b3e liquefied below -146.9degC - So, liquid nitrogen must be stored below -146.9degC(Refer: Morgan and Mikhail's Clinical Anaesthesiology, 5th edition, pg no 11 -12)