Graham's Law helps us to determine the molecular weight of an unknown gas by knowing the molecular weight of an known gas and finding experimentally their rates of effusion. Anyway it is an old method of finding the molar weight of gases.
In the preparation of bombs inseparable uranium isotopes are separated by using graham's law i.e., by sending the mixture of the uranium isotopes into a long tube the isotope with high molar weight reaches the end of the tube first and is collected. it is a lengthy process.
In industries the detection of methane gas is done by using an apparatus called the ainsin apparatus which has its origin from graham's law