the process the material in the reactor housing is pressed by the paddles into a thin layer against the wall of the reactor housing which is heated from the outside with molten salt the stripping blade following in each set of paddles scrapes the heated and partially condensed material from the walls of the reactor and mixes it with the material in the interior of the reactor whereby simultaneously the transfer of heat is effected from the heated wall via the material being stripped off an exhaust duct 20 is provided communicating with the interior of reacting housing 1 through which waste gases from the reaction may be withdrawn by means of an exhaust fan not shown means such as inlet 21 are provided associated with said duct for introducing atmospheric air into the stream of waste gases to dilute the waste gases the diluted gases may be routed to a precipitator or separator where entrained solid material is separated and the separated solids may be returned to the reactor the amount of reaction ingredients fed to the reactor is controlled so that this sequence of operations is repeated until the reaction product present in the final section of the reactor prior to the outlet is at the reaction temperature at which condensation is completed the final product obtained in this manner is conveyed over the weir 8 to the outlet 7 and discharged in carrying out reactions of this type wherein the temperature is to be variable over the course of the reaction the heating jacket is divided into separate sections the so called heating pockets which may be supplied with heating media at different temperatures a reactor according to the invention with a trough length of 320.