A yellow-orange crystalline substance which cannot be dissolved in water but can be dissolved in acetone (a type of ketone), and has the chemical formula C12H12ClNO2S. It will melt at temperatures between 66.5 and 68 degrees Celsius. &Quot;Dansyl" is an acronym for 5 dimethylamino-1 naphthalenesulfonyl. Dansyl chloride is fluorescent when it is attached to a protein or polypeptide, and is used to identify the amino acid which is on the amino terminal end of a polypeptide chain.