Hydro-extractors are a most efficient means for extracting water (p. 207) out of textile fabrics. They are made in a variety of forms by several makers. Essentially they consist of a cylindrical vessel with perforated sides, so constructed that it can be revolved at a high speed. This vessel is enclosed in an outer cage. The goods are placed in the basket, as it is termed, and then this is caused to revolve; at the high speed at which it revolves centrifugal action comes into play and the water contained in the goods finds its way to the outside of the basket through the perforations and so away from the goods. Hydro-extractors are made in a variety of sizes and forms, in some the driving gear is above, in others below the basket, in some the driving is done by belt gearing, in others a steam engine is directly connected with the basket. Figures 29 and 30 show two forms which are much in use in the textile industry. They are very efficient and extract water from textile goods more completely than any other means, as will be obvious from a study of the table below. [Illustration: Fig. 30.--Hydro-extractor.] The relative efficiency of the three systems of extracting the moisture out of textile fabrics has been investigated by Grothe, who gives in his _Appretur der Gewebe_, published in 1882, the following table showing the percentage amount of water removed in fifteen minutes:-- Yarns. Wool. Silk. Cotton. Linen. (p. 208) Wringing 44.5 45.4 45.3 50.3 Squeezing 60.0 71.4 60.0 73.6 Hydro-extracting 83.5 77 81.2 82.8 Pieces. Wringing 33.4 44.5 44.5 54.6 Squeezing 64.0 69.7 72.2 83.0 Hydro-extracting 77.8 75.5 82.3 86.0 In the practical working of hydro-extractors it is of the utmost importance that the goods be carefully and regularly laid in the basket, not too much in one part and too little in another. Any unevenness in this respect at the speed at which they are driven leaves such a strain on the bearings as to seriously endanger the safety of the machine. [Illustration: Fig. 31.--Yarn-drying Machine.] After being wrung, squeezed or hydro-extracted the goods are ready to be dried. In the case of yarns this may be done in rooms heated by steam pipes placed on the floor, the hanks being hung on rods suspended from racks arranged for the purpose. [Illustration: Fig. 32.--Cloth-drying Machine.]