Possible Clues:

• ____ acid (explosive)
• Select Richard, by the sound of it, for a CID matter
• Might a CID select old police, by the sound of it?
• By the sound of it, select old policemen for a CID matter
• By the sound of it, pick on the old 24 down in so acid a manner
• ___ acid (C6H3N3O7)
• So to select, by the sound of it, the old police is enough to make one acid
• Acid enough to select little Richard, by the sound of it
• Yellow acid used in dyeing