FILTRATION 301 



of the tube, P is the pressure, / is the length of the tube, and /* is the viscosity.* 

 In their experiments the exponent of P was found to be less than unity, and 

 they explain this as due to a closer packing of the solid particles with increase 

 of pressure. They also showed that the rate of flow is also proportional 

 to the viscosity precisely as happens in a capillary tube. 



In the experiments quoted above the material used was chromic hydrate 

 precipitated by glucose, and, although there do not appear to be any experi- 

 ments on record dealing with cane juice precipitates, there is no reason to 

 believe that similar expressions will not hold. Nothing can be said of the 

 value of the exponents except that from mill to mill the variation will be 

 large. 



The viscosity of all sugar products decreases very rapidly with rise in 

 temperature, and hence all nitrations should be carried out at as high a 

 temperature as is possible. This is especially the case with syrups. The 

 following rates of filtration were observed by Brendel 2 with beet syrups. 



Temperature C. Flow per minute. Temperature C. Flow per minute. 



2 -3 ... 3 i 40 ... 66-8 



8 ... 9-7 47 ... 91-2 



21 ... 22 'O 60 ... 146-8 



30 37*3 



Development of the Practice of Filtration. Filtration as an art may be 



said to have been established by the invention of the stocking or bag filter 

 by Cleland (patent 4949, 1824). This was improved by Taylor a few years 

 later, and his name is connected therewith to the exclusion of that of the 

 original inventor. The filter-press was originally invented as a means of 

 simultaneously pressing and filtering oil seeds and is contained in Needham's 

 patent (1669 f T ^53)- This was developed into a chamber press, with special 

 reference to sugar juices by Needham and Kite (patent 1288 of 1856), and by 

 Needham, Kite and Finzel (patent 1083 of 1856). Its functions and applica- 

 bility were greatly improved by Jacquier and Danek, whose patent (2101 

 of 1864) introduces the continuous internal conduit, the plate and frame 

 arrangement and washing out through the cake. A second important 

 patent is that of Dehne (1957 of 1878), which shows separate conduits for 

 juice and for water and locates them in lugs cast at the angles of the plates. 

 This patent shows a plate chamber press. The leaf-filter is due to an 

 American refiner, Levering, before 1845. 3 These filters are commonly called 

 " Daneks," the type having been patented by Danek (15322 of 1887). 

 From this time their use became general. A patent (376 of 1878) issued to 

 Danchell hardly differs, however, from that granted to Danek nine years 

 later. 



The use of materials, such as sand, coke, etc., is claimed in a patent 

 (9574> I ^4 2 )> issued to Crossley and Stevens, and these materials figure in a 

 number of subsequent patents. The use of sand in the European beet sugar 

 industry is generally credited to Mayer, who introduced it about 1878. 

 The later patents, of which those issued to Kostalek (9331, of 1902) and to 

 Abraham (27629 of 1902), Fig. 181, are examples, deal with special forms of 

 filters only. 



The use of kieselguhr or diatomaceous earth is claimed in a patent issued 

 to Heddle, Glen and Stewart (3116 of 1886), and in the same year Wiechmann 



* This equation is further discussed in the chapter on Centri ugels 



