Abstract The description of the metal evaporation process in the condition of an atmospheric pressure has got a special significance in the alloys smelting technologies as well as in the metallurgical waste materials treatment. The quantity of metals evaporated in the process depends on many factors from which the most important are: a kind of applied apparatus, conditions of the process, a metal bath composition and a kind of applied atmosphere. In order to state which factors have got the biggest influence on the evaporation rate it is necessary to carry out the experiments. The obtained results can be the base of a piece of information about the nature of phenomena occurring in an open system including condensate and gaseous phase. This work presents an analysis of the Fe-Sn system aimed to determine the impact of temperature (1873-2043K) and tin concentration (0.2-1.5 weight %) in liquid iron on a possibility of separation through vacuum refining. The Olette fugacity coefficient was determined for specifying the possibility of evaporating the constituent from liquid metal in the analyzed system. The calculation results were verified experimentally by vacuum induction melting of Fe-Sn alloy.