To heat metal during the (alumino)thermic welding process, a powdery mixture of metallic aluminum (Al~22%) and iron scale (Fe3O4~78%) is used as a thermite.Experience of the operation of rails welded by the thermic welding showed that every year occur from 2 to 3 fractures of thermic joints on the main tracks between stations of Latvian Railway.For the purposes of revealing stresses in the thermic weld, some scores were made tests.