Stibine is a colorless gas. It is very toxic. It has a bad smell like hydrogen sulfide. Its structure is similar to ammonia. It can be found in the Marsh test, a test for arsenic. Antimony is reacted with a mixture of zinc and hydrochloric acid in a tube, making stibine. The stibine is heated and a shiny area of antimony is made in the heated part of the tube. 