Chemical reaction. Ammonia (NH3) and hydrochloric acid (HCl) reacting in air. Diffusion of these two gases will cause a reaction at the point where the two gases meet. This reaction occurs when a white vapor ring begins forming and should take 2 to 6 minutes to start. Fumes of both NH3 (aq) and HCl (aq) are very irritating to eyes and lungs. Solutions of both can cause skin burns.