I think it would be better control of fusion reactions.
Color, the other answers arent changing the substance into something different
Avogadro's number represents the number of units in one mole of any substance. This has the value of 6.022 x 10^23 units / mole. This number can be used to convert the number of atoms or molecules into number of moles. We calculate as follows:
237g CCl4 (1 mol / 153.81 g ) (6.022 x 10^23 molecules / 1 mol ) = 9.28x10^23 molecules
A metal rail rusting in damp weather.