The solute-containing gas, or rich gas, enters the distributing space below the packing and flows upward trough the interstices in the packing countercurrent to the glow of the liquid. The packing provides a large area of contact between the liquid and gas encourages intimate contact between the phases. The solute in the rich gas and absorbed by the fresh liquid entering the tower, and dilute, or lean, gas leaves the top. The liquid is enriched in solute as it flows down the tower, and concentrated liquid, called the strong liquor, leaves the bottom of the tower through the liquid outlet. Tower packings are divided into three principal types: those that are dumped at random into the tower, those that must be staked by hand, and those known as structured or ordered packings. Dumped packings consist of unit 6 to 75 mm (1/4 to 3 in. ) in major dimension; packings smaller than 25 mm are used mainly in laboratory or pilot-plant columns. In stacked packings the unit are 50 to 200 mm (2 to 8 in.) in size. They are much less commonly used than dumped packings and are not discussed here. Dumped tower packings are made of cheap, inert materials such as clay, porcelain, or various plastics. Thin-walled metal rings of steel or aluminum are sometimes used. High void spaces and large passages for the fluids are achieved by