( ( ( The increase ) ( in pressure ) ) ( ( causes ( ( the volume ) ( of ( ( the gas ) ( inside ( the ( dropper ( to decrease ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN increase)) (PP (IN in) (NP (NN pressure)))) (VP (VBZ causes) (NP (NP (DT the) (NN volume)) (PP (IN of) (NP (NP (DT the) (NN gas)) (PP (IN inside) (NP (DT the) (NN dropper) (S (VP (TO to) (VP (VB decrease)))))))))) (. .)))
The increase in pressure causes the volume of the gas inside the dropper to decrease.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NN gas) (NNS particles)) (VP (VB heat) (PRT (RP up))))) (, ,) (NP (NN pressure)) (VP (VBP increase)) (. .)))