Hydrogen and oxygen combines in two different ways to form water and hydrogen peroxide. It is found that oxygen used up is in the ratio 8 : 16 when ${\text{H}}_{\text{2}}\text{O}$  and ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}$  are formed using 2 g of hydrogen in each case. This observation confirms to the following law of chemical combination.