The rags, having been thoroughly beaten by the teeth of the drums, pass into the duster D, consisting of a kind of hollow cylinder E, made of strong iron bars securely fastened to the circular ends F, the bars being covered with wire cloth or perforated zinc. It is made to revolve almost horizontally, a slight dip being given to it in order that the rags may be carried forward to the lower end. The bars or skeleton of the cylinder are furnished with a number of teeth securely bolted on. The whole is enclosed in a strong wooden box in which it revolves, and which serves to collect the dust passing through the wire cloth. The cylinder E is driven by the gearing G. This combined willow and duster may be used for dusting and cleaning not only rags, but almost any other kind of fibre. The willow and duster sometimes form two separate machines. The cleaned and dusted rags are now ready to be boiled, although it is the practice in some mills to give them a preliminary washing with water. The boiling may be conducted either in spherical or cylindrical boilers, or in the ordinary vomiting boilers described under Esparto. (See p. 92.) In Fig. 18 is shown, part in section and part in elevation, a spherical rag-boiler, as manufactured by Messrs. G. & W. Bertram. This boiler, of from 8 to 9 feet diameter, is supported by means of the hollow journals A on the standards B, and is made to revolve by means of the gearing C. Steam enters by the pipe D, which is fitted with a safety-valve E, and vacuum valve F. The steam on entering the boiler is distributed by means of the “baffle-plate” G. Lye enters by the pipe H. The boiler is fitted with two doors I, wherewith to fill and empty; the waste lye is run off by the cock J. L is a small blow-through cock. The false bottom K prevents the rags from choking up the cock and also serves to drain off the waste liquor. [Illustration: FIG. 18.]