The Leblanc method of making Glauber's salt (sulphate of soda) is as follows. Common salt in fine crystals is fed into a large iron still connected with several tall towers made from drain pipes, down the interior of which water is allowed to run from the tank. The requisite quantity of oil of vitriol is then run into the pan and, after the first reaction has ceased, heat is applied until all the hydrochloric acid has been evolved and the residue is a neutral sulphate of soda. The hydrochloric acid is condensed by the water in the pipes and recovered. The sulphate of soda is dug out of the pan. When this is dissolved in water and crystallised out, it is known as Glauber's salt.