A stu dy of the appea rance potentia ls and isotope abundance of tbe rare gases has been made \yith a Consolidated E ngin ee ring Corp. mass sp ectrometer as a check on the operation of th e instrument. The res ults a re comparable to previously publi s hed data. In a dd ition, some nell' experimental value of ionization poten tials have bee n obtained. Generally, good agreement of the isotope ab undance m ea surem en ts with previously published values obtain ed on other types of in strume nts and with chemica]]y determined atom ic weights, indicates a minimum of discri m ination effec ts. The relati ve yalues of th e ion current s for the rare gases we re obtai lled and p.lotted against th e atomic n um bel'. K 0 simple relation betwcen sen sitidty and atom ic Humber is evident.