Sometimes yarns or cloths have to be passed through a soap-bath after being dyed in order to brighten up the colours or develop them in some way. In the case of yarns this can be done on the reel washing (p. 205) machines such as are shown in figure 25. In the case of piece goods a continuous machine in which the washing, soaping, etc., can be carried on simultaneously is often employed. Such a machine is shown in figure 28. It consists of a number of compartments fitted with guide rollers, so that the cloth passes up and down several times through the liquors in the compartment; between one compartment and another is placed a pair of squeezing rollers. The cloth is threaded in a continuous manner, well shown in the drawing, through the machine; in one compartment it is treated with water, in another with soap liquor, and another with water, and so on, and these machines may be made with two, three or more compartments, as may be necessary for the particular work in hand. As seen in the drawing the cloth passes in at one end, and out at the other finished. It is usually arranged that a continuous current of the various liquors used flows through the various compartments, thus ensuring the most perfect treatment of the cloths. [Illustration: Fig. 28.--Soaping and Washing Machine.] DRYING. (p. 206) Following on the washing comes the final operation of the dyeing process, that of drying the dyed and washed goods. Now textile fabrics of all kinds after they have passed through dye-baths, washing machines, etc., contain a large amount of water, often exceeding in amount that of the fabric itself, and to take the goods direct from the preceding operations to the drying plant means that a considerable amount of fuel must be expended to drive off this large amount of water. It is therefore very desirable that the goods be freed from as much of this water as possible before they are sent into any drying chambers, and this may be done in three ways, by wringing, squeezing and hydro-extracting. The first two methods have already been described (pp. 198, 199) and need not again be alluded to, the last needs some account. [Illustration: Fig. 29.--Hydro-extractor.]