▁air ▁after ▁met als ▁had ▁been ▁calc ined . ▁He ▁showed ▁that ▁this ▁resid ual ▁air ▁supported ▁neither ▁comb ust ion ▁nor ▁resp iration ▁and ▁that ▁approximately ▁five ▁volumes ▁of ▁this ▁air ▁added ▁to ▁one ▁volume ▁of ▁the ▁de ph log istic ated ▁air ▁gave ▁common ▁atmos pher ic ▁air . ▁Common ▁air ▁was ▁then ▁a ▁mixture ▁of ▁two ▁distinct ▁chemical ▁species ▁with ▁quite ▁different ▁properties . ▁Thus ▁when ▁the ▁re vised ▁version ▁of ▁the ▁E aster ▁Mem oir ▁was ▁published ▁in ▁ 1 7 7 8 , ▁Lav ois ier ▁no ▁longer ▁stated ▁that ▁the ▁principle ▁which ▁combined ▁with ▁met als ▁on ▁calc ination ▁was ▁just ▁common ▁air ▁but ▁" nothing ▁else ▁than ▁the ▁health iest ▁and ▁pur est ▁part ▁of ▁the ▁air " ▁or ▁the ▁" em in ently ▁res pi rable ▁part ▁of ▁the ▁air ". ▁The ▁same ▁year ▁he ▁co ined ▁the ▁name ▁o xygen ▁for ▁this ▁constitu ent ▁of ▁the ▁air , ▁from ▁the ▁Greek ▁words ▁meaning ▁" ac id ▁former ". ▁He ▁was ▁struck ▁by ▁the ▁fact ▁that ▁the ▁comb ust ion ▁products ▁of ▁such ▁non met als ▁as ▁sul fur , ▁ph osph orus , ▁char co al , ▁and ▁nit ro gen ▁were ▁acid ic . ▁He ▁held ▁that ▁all ▁ac ids ▁contained ▁o xygen ▁and ▁that ▁o xygen ▁was ▁therefore ▁the ▁acid ifying ▁principle . ▁ ▁D ism ant ling ▁ph log ist on ▁theory ▁ ▁Lav ois ier ' s ▁chemical ▁research ▁between ▁ 1 7 7 2 ▁and ▁ 1 7 7