This video demonstrates a simple chemical reaction between ammonia (NH3) and hydrochloric acid (HCl) to form the salt ammonium chloride (NH4Cl). When the reaction takes place between the two reactants as their vapors mix in the air the solid ammonium chloride product is formed in flowing trails ideal for beautiful smoke photography. One of the comments I have so far received on YouTube suggested it would be great for use with lasers! What a great idea! Maybe I'll make a followup video.