Abstract: An elongated web is formed into the general shape of a longitudinally extending helix having a horizontal succession of turns each of which is partially submerged in a bath of treatment liquid. A guide in the form of an auger or rake keeps the turns apart and a drive element located above the guide is rotated continuously to turn the helix in the bath. A generally horizontal but inclined plate has an upper edge just below the drive element. A pump draws the treatment fluid from the bottom of the vessel and delivers it to the upper edge of the plate so as to form thereon a downwardly gravitationally flowing sheet of treatment liquid on which the turns of the web are supported as they pass from the drive element on one side of the elongated vessel to the other side thereof.