In the monograph, the author summarises the results obtained in research and investigations of the gas-liquid metal system at temperatures typical of electric arc welding and electrometallurgy processes. Special attention is given to the problems of sorption of diatomic homonuclear gases, especially nitrogen from electric arc plasma, by metal melts. It is shown that when the metal absorbs the gas from plasma the system does not reach the thermodynamic equilibrium state. Investigations were carried out into processes taking place in the gas-plasma layer bordering with the metal. These processes determine the gas content of liquid steel.