1,215,709. Washing apparatus for treating tows with liquids. MONSANTO CO. 27 Dec., 1967 [29 Dec., 1966], No. 58729/67. Heading B5B. [Also in Division D1] Apparatus for treating a moving tow with a liquid, especially a tow washer, useful in wetspinning processes, comprises an inlet stage, an intermediate stage, and an outlet stage connected together in series, these stages forming a passageway for the movement of water and a tow to be washed, wherein water is forced into the inlet stage and through the passageway to wash a thin ribbon of synthetic filaments moving through the passageway, the inner walls of the intermediate stage on opposite sides of the tow being formed by a plurality of interconnecting plane and curved surfaces which serve to deflect the heated water back and forth through the moving tow, the surface configuration of the wall on one side of the tow being a mirror image of that on the other side of the tow with one of the walls being displaced longitudinally relative to the other and rotated 180 degrees, the surface configuration being defined by the plane and curved surfaces beginning in the inlet stage and extending through the intermediate stage to the outlet stage, the arrangement being such that washing of the tow takes place in each of the three stages. As shown, a tow washer 11 has an upper portion 12, a lower portion 13 and side walls 14 which together form a chamber through which water and the tow pass, said chamber having a width slightly greater than the width of said tow. The vertical dimension of the opening between the upper portion 12 and the lower portion 13 is defined by spaced horizontal planes 24 and 25, said planes being spaced apart a distance A. The upper portion 12 has a first flat surface 30 lying in the upper plane 24 and extending downstream (with reference to the flow of water) from the inlet end of the intermediate stage a distance L, and a second flat surface 31 extending downstream therefrom and positioned at an angle # relative to said upper plane 24, the second flat surface having a length M. The upper portion 12 also has a concave cylindrical surface 32 extending laterally thereacross, said cylindrical surface having a radius R. The downstream extremity of said cylindrical surface ends in a sharp edge 35 lying in the upper plane 24 and the axis of the cylindrical surface 32 lies in the upper plane 24 and is spaced downstream from the entrance end of the intermediate stage a distance N. The upper portion 12 also has a third flat surface 33 at a tangent to said cylindrical surface 32 and extending upstream (with reference to the flow of water) at an angle α relative to the upper plane 24. Further, the upper portion 12 also has a convex arcuate surface 34 leading from the downstream end of the second flat surface 31 to the upstream end of the third flat surface 33. Arcuate surface 34 is at a tangent to said second and third flat surfaces 31 and 33 and has a radius R. Preferably A equals 1À5 to 15 times the thickness of the tow, L = A to 10A, M = 4-18A, N = 16-50A, R = 4-14A, R<SP>1</SP> = 2-10A, O = 1À5-10A, # = 0À5-8 degrees and α = 10-90 degrees, where O is the distance between the sharp edge 35 on the upper portion 12 and the plane of the third flat surface 33<SP>1</SP> on the lower portion 13. The lower portion 13 has an upper surface which is a mirror image of the lower surface of the upper portion 12; and has the surface configuration thereof so displaced longitudinally a distance P relative to the upper portion 12 that the sharp edge 35 at the downstream extremity of the cylindrical surface of the lower portion 13 is positioned a distance O from said third flat surface 33 of said upper portion 12, and preferably O = 2-5A; and P = A-30A. The most suitable values are as follows: A = 2-8 times the thickness of the tow, L = 2-6A, M = 5-9A, N = 22-28A, R = 6-9A, R<SP>1</SP> = 3-5A, O = 2-4A, # = 1À5-3 degrees, α = 35-55 degrees, and P = 6-10A. In operation, the tow 17 is advanced through the chamber formed by the upper and lower portions 12 and 13 and the side walls 14 as shown in Fig. 1. Water is forced into the apparatus from the inlet opening 21 through the orifice 23, and is divided into two more or less equal streams, each of which travels from the upper end of the orifice opening in opposite directions to the outlet opening 22. The surface configuration of the upper and lower portions forces the water to sweep back and forth through the flat ribbon of filaments from one side thereof to the other. The velocity of the water and the configuration of the upper and lower portions ensures that every filament in the tow will be separated from adjacent filaments so that the tow will be thoroughly penetrated by the water in only a short distance of travel. Thus, the washing operation is made significantly more efficient. The surface configurations of the upper and lower portions 12 and 13 ensure that the water will follow a roughly sinusoidal path in flowing through the apparatus. Because of the close clearance between the filaments in the tow, the water is quite turbulent in its passage through the tow 17. Hot water is preferred, but using the apparatus of the invention, completely adequate washing of a moving tow of synthetic filaments obtained in a wet spinning process may be obtained with water at room temperature.