Peroxide of hydrogen is made by suspending barium peroxide in water and adding the requisite quantity of dilute sulphuric acid. Barium sulphate is precipitated and hydrogen peroxide remains in solution and is concentrated at ordinary temperature in a partial vacuum over sulphuric acid. Seventeen parts of barium peroxide will require 10 parts of strong sulphuric acid, previously diluted with 40 parts of water, for its decomposition.