( ( ( dense gas ) ( fades faster ) ) ( , ( ( low ( density gas ) ) ( ( fades slower ) . ) ) ) )
(ROOT (S (S (NP (JJ dense) (NN gas)) (VP (VBZ fades) (ADVP (RBR faster)))) (, ,) (NP (JJ low) (NN density) (NN gas)) (VP (VBZ fades) (ADJP (JJR slower))) (. .)))
dense gas fades faster, low density gas fades slower.
(ROOT (S (NP (NNS Gases)) (VP (VBP have) (NP (DT the) (JJS lowest) (NN density))) (. .)))