Eliot compares the poet's thinking to a catalyst and the process of poetry invention to a chemical reaction. The poet's mind is required for new combinations of feelings and experiences to occur, yet it does not alter during the process of poetic combination. Just as with a chemical reaction, once the first molecule is combined with another of its kind it cannot recombine with itself. Catalysts are substances that initiate or speed up a chemical reaction without being consumed by it. For example, when hydrogen peroxide is mixed with an alkaline solution it will react to produce water and oxygen. However, if an acid is added to this mixture it will destroy the acidity of the solution and prevent further reaction until a base is again added. The catalyst used in this case was hydrochloric acid which initiates the reaction by breaking down the hydrogen peroxide into two molecules of water plus one molecule of oxygen and one molecule of chloride ion. In chemistry, a catalyst can also be used to promote the formation of certain compounds. For example, iron filings or charcoal can be added to a solution of sodium carbonate and potassium hydroxide to create a white precipitate that is composed primarily of calcium oxide and potassium sulfate. Without a catalyst, these chemicals would only form solid compounds like chalk or saltwater. Poetry is a product of the human imagination.