The mass of nitrogen per gram in hydrazine is exactly one and half the mass of nitrogen in the compound ammonia. The fact illustrates the

$\mathrm{Hydrazine} \mathrm{Formula}={\mathrm{N}}_2{\mathrm{H}}_4$

$\mathrm{Ammonia}={\mathrm{NH}}_3$

These are different compounds made up of only two same elements. So, these compounds obey law of multiple proportions.