The　effect　of　carbon　on　nitrogen　solubility　in　slag　was　investigated　for　the　ternary　CaO-MgO-SiO2　and　the　quaternary　Al2O3-CaO-MgO-SiO2　slag　systems　at　1　873　K　under　controlled　oxygen　and　nitrogen　potentials.　Gas-slag　equilibration　experiments　were　conducted　using　molybdenum　and　graphite　crucibles.　In　the　absence　of　carbon,　the　nitrogen　solubility　was　very　low.　The　presence　of　carbon　greatly　increased　the　nitrogen　solubility　in　slag.　The　total　nitrogen　content　was　found　to　increase　with　SiO2　and　MgO　concentration　for　the　carbon　saturated　slags.　Low　levels　of　cyanide　were　found　by　wet　chemistry　with　considerable　uncertainty.　The　results　analyzed　by　different　methods　ruled　out　cyanide　formation　being　the　main　reason　for　the　large　increase　in　nitrogen　solubility　in　the　presence　of　pure　carbon.