Sentence:  A hydrostatic head correction has been neither necessary nor applicable in the determination of vapor pressures or temperatures for the bulk liquid <WSD>helium</WSD> . 
Meaning of the word marked with <WSD> tags:  a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)