CHAPTER XII. 



THE DIFFUSION PKOCESS. 



In the process described in the previous chapter the juice is extracted 

 from the cane by rupture of the cells which contain the juice. In the 

 diffusion process an entirely different system of extraction is carried out, the 

 principle of which is as under : If a solution of a soluble body such as sugar 

 contained in a cell, the walls of which consist of some porous material, for 

 example, unglazed earthenware, parchment, or the woody cells of which 

 plants are built up, be immersed in a vessel of water, it is found that the 

 sugar solution passes out through the porous wall into the water and that 

 water enters the cell ; this process continues until the solution on both sides 

 of the cell is the same. It is not all bodies that possess this property. Those 

 which do not, for example, gummy bodies, are termed colloids, and in general 

 it is found that it is crystalline bodies that possess the property of passing 

 through a porous membrane ; to this phenomenon the name of osmosis or 

 diffusion is given. 



The sugar cane consists of a vast number of cells, in the interior of which 

 the juice is contained ; and the diffusion process applied to the extraction of 

 juice consists of systematically allowing the juice in these cells to diffuse into 

 water or diluted juice. In the diffusion process the cane is cat into fine slices 

 about one-twentieth of an inch thick. These slices, technically called chips, 

 are placed in vessels known as cells or diffusers, and are systematically washed 

 until a very high degree of exhaustion is obtained. The system of working 

 is roughly this : Suppose that there are twelve cells in use, these are all 

 connected so that juice from one cell can be passed on to the next succeeding 

 one ; into a cell fresh chips are introduced ; water that has passed over eleven 

 sets of chips is forced into this cell, and after diffusion has taken place a charge 

 of juice is withdrawn, and water which has passed over ten sets of chips takes 

 its place. This process continues until water alone enters the cell. The 

 highly diluted juice passes on in the above-described routine, and the chips are 

 discharged to be, in general, crushed in a mill to remove water before use as 

 fuel. 



The essential parts of a diffusion plant are described below. 



Cane Cutter. A type of cane cutter that has been largely used is 

 shown in vertical section in Fig. 183; on a vertical spindle b, belt-driven from 

 the pulley d, by means of the bevel wheels c, is carried a disc e. The whole 



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