Undercertain conditions, the components of molten iron such as silicon, manganese,iron and in case of nodular iron, magnesium, are prone to form oxides and othernon-metallic compounds. These compounds may also be formed during desulphurising,refining and alloying treatments. The non-metallic compounds are insoluble iniron tending to remain suspended in the melt. They have the tendency of floatingtothesurfacewhen a number ofparticles havecoalesced.