# The usage of 'limiting composition'

Blue bronzes, with limiting composition $\ce{A_{0.3}MoO3}$ that is, $\ce{A_3Mo10O30}$.
For example, iron(II) sulfide can have a ratio from about $\ce{Fe_{$0.8$}S}$ to $\ce{FeS}$. So in LCM terms, the formula varies continually from $\ce{Fe4S5}$ through $\ce{FeS}$, including $\ce{Fe9S10}$, $\ce{Fe19S20}$ and so forth, all with similar physical and chemical properties.