The following data are available.

i) % of Mg in Mg and in $\text{MgC}{l}_2$            

ii) % of C in CO & ${\text{CO}}_{\text{2}}$

iii) % of Cr in ${\text{K}}_{\text{2}}{\text{\hspace{0.17em}Cr}}_{\text{2}}{\text{\hspace{0.17em}O}}_7$and ${\text{K}}_{\text{2}}{\text{CrO}}_{\text{4}}$and   

iv) % of Cu isotopes in Cu metal.

The law of multiple proportions may be illustrated by data.