412 CHAPTER XX 



not survived, though once in extended use. It is illustrated as formerly 

 made in Fig. 257. 



It is curious to note that the differences between Bessemer's patent 

 (13202, 1850) and Nind's patent (13416, of 1850) are very closely paralleled 

 by similar differences in those of Weston and Hepworth. 



Two other types of machine may be mentioned. Lafferty's patent 

 (235 of 1869) caused the solid spindle carrying the basket to pass through 

 an intermediate hollow shaft, elastic material being interposed between the 

 shaft and the spindle. The spindle was extended through and beneath the 

 basket, terminating at its extremity in an elastic bearing. In Cottle's patent 

 (1350 of 1872) the solid spindle carrying the basket terminated in a hemi- 

 spherical piece resting on a counterpart bearing. This device was further 

 developed in Tolhurst's patent (255 of 1878), who employed a spindle with a 

 cone-shaped termination resting on a cone-shaped base, so that the machine 

 was free to rock in all directions, the amplitude of the movement being 

 restrained by rubber cushions. These types have been largely used in the 

 past, and the last-named machine, though not employed in the sugar industry, 

 finds an extended use in other trades. 



The Centrifugal Basket and Screen. The centrifugal basket consists 

 of a vertical cylinder partly open at top and bottom, as indicated in Fig. 256. 

 It is usually constructed of steel and is securely attached to the revolving 

 spindle. 



As found in the raw sugar industry, the sizes of the basket are 

 3O-in. X i8-in., 36-in. x i8-in., 4o-in. X2Q-in., 4o-in. X24-in., 42-in. x 2O-in., 

 42-in. X 24-in. and 48-01. X 24-in. ; the thickness of the shell is usually 

 T V m - to J-in. The shell is perforated to allow the molasses to pass, the 

 perforations being usually f-in. to i-in. pitch and about y^-in. diameter. These 

 dimensions, of course, vary among the different makers. To give additional 

 strength, the shell is reinforced with circumferential hoops of steel ; in a 

 42-in. machine there are usually eight of these hoops, one inch deep and one- 

 quarter inch wide. 



The bottom of the basket is usually made horizontal or sloping slightly 

 downwards, with a central opening for the discharge of the dried sugar ; 

 when running this opening is closed by a valve. 



The lip of the basket is horizontal or slightly sloping upwards ; its duty 

 is to prevent the massecuite from climbing upwards under the action of the 

 centrifugal force. The width of the lip is about six inches and varies, of 

 course, as among different makers. The contents or charge of the basket 

 is determined by the volume defined by the shell, the lip, and a vertical 

 dropped from the inner edge of the lip. It is the practice, however, to charge 

 the basket while it is already in motion, so that during the process of charging 

 molasses is already being removed, and thus the capacity or charge is in- 

 creased. 



The screen which serves to retain the crystals is made of perforated 

 copper or brass sheet, or is woven. The perforations may be circular or 

 elongated conical holes, as first proposed by Gwynne (patent 13577, I ^5 1 )- 

 The woven material is suitable for very fine sugars, and the perforated for 

 coarse material. The perforations are usually about one-fortieth of an inch, 

 and are spaced twenty to the inch. Between the wall of the basket and 

 the screen is interposed a very coarse woven screen, with mesh at least one- 

 quarter inch, upon which the screen rests. In its absence the perforated 



