In research conducted by the United States Bureau of Mines, the Sn-C and Al-Sn-C phase diagrams were determined over the temperature range of 1550 degrees C to 2300 degrees C by chemical analysis of alloys saturated with carbon within sealed graphite crucibles. Carbon forms a dilute solution in tin described by log [at. pct C] = 2.9767-12,082.35/T, where T is temperature in Kelvin. Isothermal sections for the ternary system were determined at intervals of 150 degrees C over the range of temperatures investigated. The univariant points on the 1700 degrees C, 1850 degrees C, and 2000 degrees C isotherms were determined by metallographic examination of rapidly cooled alloys to be about 34Al-66Sn-0.1C, 49.7Al-49.7Sn-0.5C, and 70Al-27Sn-2.8C, respectively, where all concentrations are atomic percent. Graphite and A14C3 (decomposition temperature 2156 degrees C) were the only solid phases observed at these temperatures. The excess partial Gibbs energy for dissolved C in liquid Al-Sn-C solutions in equilibrium with C, as calculated from the experimental solubilities, is G C e = -RT ln x = y2[176.860 - 55.42T - (224,200 - 110.84T)x] + (231,400 - 18.700T)z2 + yz[151,860 - 8.423T + (19,400 - 8.4867)z + (56,100 - 57.6577)yz - (39,800 - 40.904T)yz2], J/g · atom where R is the gas constant, T is the temperature in Kelvin, and x, y, and z are the atomic fractions of C, Al, and Sn, respectively. The equation also is a good approximation for liquid solutions in equilibrium with A14C3 within about 100 degrees C of the decomposition temperature.