on ▁given ▁off ▁by ▁burning ▁bodies ▁and ▁resp iring ▁animals , ▁the ▁greatly ▁en hanced ▁comb ust ion ▁of ▁subst ances ▁and ▁the ▁greater ▁ease ▁of ▁breath ing ▁in ▁this ▁air ▁were ▁explained . ▁ ▁P ione er ▁of ▁sto ichi ometry ▁Lav ois ier ' s ▁research es ▁included ▁some ▁of ▁the ▁first ▁truly ▁quant itative ▁chemical ▁experiments . ▁He ▁carefully ▁we ighed ▁the ▁react ants ▁and ▁products ▁of ▁a ▁chemical ▁reaction ▁in ▁a ▁se aled ▁glass ▁vessel ▁so ▁that ▁no ▁g ases ▁could ▁escape , ▁which ▁was ▁a ▁cru cial ▁step ▁in ▁the ▁adv ancement ▁of ▁chem istry . ▁In ▁ 1 7 7 4 , ▁he ▁showed ▁that , ▁although ▁matter ▁can ▁change ▁its ▁state ▁in ▁a ▁chemical ▁reaction , ▁the ▁total ▁mass ▁of ▁matter ▁is ▁the ▁same ▁at ▁the ▁end ▁as ▁at ▁the ▁beginning ▁of ▁every ▁chemical ▁change . ▁Thus , ▁for ▁instance , ▁if ▁a ▁piece ▁of ▁wood ▁is ▁burn ed ▁to ▁as hes , ▁the ▁total ▁mass ▁remains ▁un changed ▁if ▁g ase ous ▁react ants ▁and ▁products ▁are ▁included . ▁Lav ois ier ' s ▁experiments ▁supported ▁the ▁law ▁of ▁conservation ▁of ▁mass . ▁In ▁France ▁it ▁is ▁taught ▁as ▁Lav ois ier ' s ▁Law ▁and ▁is ▁par ap hr ased ▁from ▁a ▁statement ▁in ▁his ▁Tra ité ▁É lé ment aire ▁de ▁Ch im ie : ▁" Nothing ▁is ▁lost , ▁nothing ▁is ▁created , ▁everything ▁is ▁transformed ." ▁Mik h ail ▁L omon os ov ▁( 1 7 1 1 – 1 7