Chlorine dissolved paper rattle (7)
I believe the answer is:
clapper
'rattle' is the definition.
(thesaurus)
'chlorine dissolved paper' is the wordplay.
'chlorine' becomes 'Cl' (chemical symbol).
'dissolved' indicates anagramming the letters.
'paper' anagrammed gives 'apper'.
'cl'+'apper'='CLAPPER'
(Other definitions for clapper that I've seen before include "appreciative person" , "Appreciative member of audience" , "Bell's tongue" , "part of the "Ring Cycle"?" , "enthusiastic type" .)