“…In this way, metastable liquids are avoided in the system CaSiO~-MnSiO~-PbSiO~. However, the quaternary solid solution is unstable due to the volatility of lead so that the reaction: fi(Ca,Mn)SiO~ss -F Pb ~ § fl(Ca,Mn,Pb)SiO~ss [1] cannot be expected to be very successful. The alternative reaction: a(Ca,Pb)SiO~ss -F Mn ~*-~ fl(Ca,Mn,Pb)SiO~ss [2] should be more successful due to the greater stability of lead in a(Ca,Pb)SiO.ss than in fi(Ca,Mn,Pb) SiO,ss.…”