premise: When values of temperature derived with this instrument were compared with the accepted values associated with liquid <mask> 4 vapor pressures , differences of about 10 and 7 millidegrees respectively were found .
hypothesis: the proper context for <mask> here should be 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)