Abstract: An apparatus for the treatment of timber comprises a vessel having at least three chambers arranged in series for passage of the timber therethrough on conveyor belts or the like. There is means for drawing a vacuum in each of the end chambers and means for spraying the timber with a preservative liquid in an intermediate chamber, the vacuums being maintained during passage of the timber through the end chambers, by means of seals which are arranged to close and open automatically as the timber enters and leaves the respective vacuum chambers.