( ( role ( of ( ( ( ash ( in ( converting sulfur ) ) ) dioxide ) ( ( ( ( to ( sulfur trioxide ) ) and ) then ) ( to ( sulfuric acid ) ) ) ) ) ) ; )
(ROOT (NP (NP (NP (NN role)) (PP (IN of) (NP (NP (ADJP (JJ ash) (PP (IN in) (S (VP (VBG converting) (NP (NN sulfur)))))) (NN dioxide)) (PP (PP (TO to) (NP (NN sulfur) (NN trioxide))) (CC and) (ADVP (RB then)) (PP (TO to) (NP (JJ sulfuric) (NN acid))))))) (: ;)))
role of ash in converting sulfur dioxide to sulfur trioxide and then to sulfuric acid;
(ROOT (S (NP (NNP Sulfur)) (VP (MD can) (VP (VB combine) (PP (IN with) (NP (NN oxygen))) (S (VP (TO to) (VP (VB produce) (NP (NN sulfur) (NN trioxide))))))) (. .)))