Hydrogen peroxide is a colorless liquid that has a bitter taste and is caustic to skin. Pure H₂O₂ is a thick liquid like syrup that it quickly decomposes into oxygen and water. Usually it is sold in weaker solutions (most commonly 3 percent), diluted with water.

In nature, hydrogen peroxide occurs only in trace amounts, mostly in snow and rain. It is produced in the atmosphere during lightening storms. Additionally, it can be manufactured easily using electrochemical processes. However, concentrated hydrogen peroxide can start fires if dripped onto wood or paper, so it must be carefully handled and stored.

One of the first things that Louis Thenard found out about hydrogen peroxide was that it attacks the skin, producing painful blotches. Fortunately, this effect wore off completely within a few hours. Thenard had tried for many months to formulate the chemical, now known to be H...