▁which ▁combined ▁with ▁met als ▁on ▁calc ination ▁and ▁increased ▁the ▁weight ▁might ▁be ▁Black ' s ▁fixed ▁air , ▁that ▁is , ▁CO 2 . ▁ ▁Joseph ▁Pri est ley ▁ ▁In ▁the ▁spring ▁of ▁ 1 7 7 4 , ▁Lav ois ier ▁carried ▁out ▁experiments ▁on ▁the ▁calc ination ▁of ▁tin ▁and ▁lead ▁in ▁se aled ▁vessels , ▁the ▁results ▁of ▁which ▁conclus ively ▁confirmed ▁that ▁the ▁increase ▁in ▁weight ▁of ▁met als ▁in ▁comb ust ion ▁was ▁due ▁to ▁combination ▁with ▁air . ▁But ▁the ▁question ▁remained ▁about ▁whether ▁it ▁was ▁in ▁combination ▁with ▁common ▁atmos pher ic ▁air ▁or ▁with ▁only ▁a ▁part ▁of ▁atmos pher ic ▁air . ▁In ▁October ▁the ▁English ▁chem ist ▁Joseph ▁Pri est ley ▁visited ▁Paris , ▁where ▁he ▁met ▁Lav ois ier ▁and ▁told ▁him ▁of ▁the ▁air ▁which ▁he ▁had ▁produced ▁by ▁he ating ▁the ▁red ▁cal x ▁of ▁mer cur y ▁with ▁a ▁burning ▁glass ▁and ▁which ▁had ▁supported ▁comb ust ion ▁with ▁extreme ▁vig or . ▁Pri est ley ▁at ▁this ▁time ▁was ▁uns ure ▁of ▁the ▁nature ▁of ▁this ▁gas , ▁but ▁he ▁felt ▁that ▁it ▁was ▁an ▁especially ▁pure ▁form ▁of ▁common ▁air . ▁Lav ois ier ▁carried ▁out ▁his ▁own ▁research es ▁on ▁this ▁peculiar ▁subst ance . ▁The ▁result ▁was ▁his ▁mem oir ▁On ▁the ▁Nature ▁of ▁the ▁Princi ple ▁Which ▁Com b ines ▁with ▁Met als ▁during ▁Their ▁Cal c ination ▁and ▁In cre ases ▁Their ▁We ight , ▁read ▁to ▁the ▁Academy ▁on