An extremely unstable gas, PbH₄, said to be formed by the action of acids on magnesium–lead alloys. It was first reported in 1924, but doubts were subsequently expressed about the existence of the compound. Although the existence of plumbane has now been definitively established, its instability makes the determination of its properties very difficult to establish. It demonstrates the declining stability of the hydrides in group 14. More stable organic derivatives are known; e.g. trimethyl plumbane, (CH₃)₃PbH.