Abstract: A continuous reactor for viscous materials that give off volatile matter during operation has two rows of agitation rotors mounted staggeredly and with a phase angle of 90.degree. to each other on a parallel pair of shafts. Each of the agitation rotors consists of a pair of annular brackets arranged symmetrically across the axis of one shaft in a figure eight pattern, and a pair of scraper plates attached edgewise to the free ends of the brackets, one for each, at right angles to the brackets and in parallel with the shaft. The shafts are spaced apart so that the rotors on each shaft can revolve with their free ends passing close by the other shaft as well as part of the surrounding wall of the casing.