302 



CHAPTER XVII 



was granted a patent in America (343287). Soxhlet, to whom the credit 

 for the introduction of this material is generally given, took out a patent 

 much later (212 17 of 1892) . Casamaj or's proposal to use sawdust is contained 

 in patent 257 of 1883. 



Filtration through fine wire gauze is claimed in a patent (11312, 1846), 

 and again much later by Robertson and Watson (patent 974 of 1873). 



Filtration under centrifugal force through flannel is claimed in Bessemer' s 

 patent (13202, 1850). 



The Bag or Stocking Filter. The bag filter of Cleland (patent 4949, 

 1824), usually known as the Taylor filter, consists of a sheath of strong woven 

 material, one end of which is closed by tying. The other end is secured 

 to the wide end of a hollow metal cone. Inside the sheath may be placed a 

 second wide bag turned upon itself several times, and which forms the 

 filtering material, the outer sheath in this case merely serving to support 

 the inner one. This method is described in Schroeder's patent (8675, 1840). 

 The narrow ends of the cones are secured in a horizontal frame, the whole 

 system of frame and bags being contained in a rectangular iron casing. 

 The usual length of the bags is six feet. The sides of the chamber project 



IV, 



FIG. 174 



FIG. 175 



FIG. 176 



above the frame on which the bags are carried and thus form a reservoir, 

 into which is run the material to be filtered. Generally filtration takes 

 place under gravity only, but pressure types have been used, the pressure 

 being obtained either by forming a vacuum in the chamber or by causing an 

 air pressure on the surface of the liquid. The bag filter survives only 

 occasionally in the cane sugai industry. 



The Chamber Press. The chamber press is found in two forms, the plate 

 and frame press, and the plate press. The form described below is an angle 

 feed washout plate and frame press. Fig. 175 shows an elevation of the 

 frame. It is formed of a skeleton of square shape, and is up to ij inches in 

 thickness. The thickness of the frame determines the thickness of the 

 cake of material, and this is in turn determined by the nature of the preci- 

 pitate to be filtered off. At horizontally opposite corners are arranged the 

 lugs or ears, in which are formed transverse openings j and w t the upper one 

 of which communicates by a channel, a, with the space bounded by the 

 inner surfaces of the frame. Fig. 174 is an elevation of one of the two kinds 

 of plates called the juice plate. It is a casting of over-all dimensions corres- 

 ponding to those of the frame and with transverse openings j and w registering 

 with those of the frame ; neither of these openings communicates with the 

 interior of the press. The other plate, Fig. 176, is called the water plate, 



