In the double displacement reaction of a metal sulfide with an acid, we will start out with a small amount of sodium sulfide. We will add an aqueous solution of hydrochloric acid. The sodium sulfide and hydrochloric acid react to produce hydrogen sulfide. The hydrogen sulfide is released as a gas. We can test for the presence of hydrogen sulfide by bringing in a strip of wet lead acetate paper. The hydrogen sulfide reacts with the lead acetate paper to form lead sulfide, which is a brown black precipitate.