CHAPTER XII 

 THE DIFFUSION PROCESS 



IN the early part of the nineteenth century a German professor, Goettling, 

 proposed to extract the juice of the beetroot by systematic washing, and 

 his scheme was operated at Karlsruhe, by Haber and Schutzenbach. In 

 France the earliest pioneer of this process was Matthieu de Dombasle, whose 

 French patent is 7981 of 1831. The earliest British patent and the first one 

 mentioning the cane is that of Watson (7124, 1836) which describes a one-cell 

 counter-current process. Constable's British patent, communicated to him 

 by Michel, is 10171, 1844, and. it describes a process in which the cane is 

 transferred in perforated baskets from cell to cell. This patent correctly 

 describes the mechanism of diffusion through a permeable membrane, and is 

 the one which was unsuccessfully operated in Guadeloupe by Bouscaren 

 about this time. The actual introduction of diffusion as a commercial 

 process is due to Robert, the manager of a beet sugar factory at Seelowitz, in 

 Austria. His British patents are 594 and 3187 of 1866, taken out by Minchin, 

 who operated diffusion successfully at Aska, in India. 



From the time of its first successful operation, the diffusion process 

 became rapidly established in the beet sugar industry, and its operation 

 remains now as originally executed. The only developments have been 

 some attempts to put into operation continuous diffusion processes, such as 

 those of Kessler (British patent 15355 of 1902) and of Rak (British patent 

 16905 of 1901). The latter is in use in a few factories. 



In a diffusion process proper, the plant cell is not ruptured, and advantage 

 is taken of the property possessed by crystalloids of passing through a cell 

 wall, or membrane, when water or a solution more dilute than that contained 

 in the cell is in contact with the exterior of the cell wall. In this way the 

 bodies of a colloid nature which do not possess this property are retained 

 within the cell. Independently of diffusion through a cell wall, all solutions 

 in contact tend to become of equal concentration, and the process is physi- 

 cally of the same nature as diffusion, such an action obtaining when the cell 

 wall is ruptured. 



This property occurred in the older processes, such as that of Dombasle, to 

 which the term " maceration " was originally applied, and this term or some 

 equivalent such as " lixiviation," should be applied to those processes which 

 deal with comminuted material such as bagasse, since in the absence of a 

 cell wall or other permeable membrane diffusion proper does not obtain. 



In the sugar cane industry numerous plants were erected in Spain, 

 Egypt, Louisiana, Mauritius, Brazil, Demerara, Java, Hawaii, and the West 

 Indies. Very few of them now remain, and most of those that were erected 

 met with financial disaster. The causes which led to failure were both 

 technical and economic, and may be briefly summarized : 



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