CHAPTER XIII 



The Action of Heat, Alkalies and Acids on 

 Sugars and Cane Juices 



In the process of sugar manufacture the cane juice is subjected to the in- 

 fluence of an elevated temperature, and to the action of hme. In some 

 processes sulphurous and phosphoric acids are also employed. The action 

 of these agents, together with some other connected points, is discussed in 

 this chapter. 



Cane juice, as it leaves the mill, consists of a turbid solution of cane 

 sugar, reducing sugars, bodies of unknown constitution known as " gums," 

 salts of both organic and inorganic acids, mainly potash salts, colouring 

 matters, albuminoids, matter in a colloid condition, suspended particles of 

 fibre and dirt, and a variety of other bodies. 



The Colloids of Cane Juice. — WTien all the grosser particles of suspended 

 matter in a cane juice have been removed by straining through glass wool, 

 there remains a turbid liquid, the turbidity of which is due to matter in the 

 colloid state. The following observations were made by the writer^. The 

 colloids may be separated in the cold by filtration through asbestos. The 

 filtration is very slow and only 5 c.c. of juice can be filtered through an area of 

 1 sq. cm. before the asbestos mat is clogged. The filtrate obtained is quite 

 bright, and on heating never gives more than a trace of precipitate, indicat- 

 ing that filtration removes the same bodies as are coagulated by heat. The 

 quantity of colloids thus separated by filtration amounts to from 0-15 t.i 

 0-25 gram per 100 c.c. of juice. After coagulation b3^ heat, the colloids 

 do not revert to the colloid condition on cooling, but after coagulation by 

 alkalies the colloid state again appears on neutralization. The colloids 

 are not precipitated by electrolytes except by calcium chloride in very large 

 quantity, and are hence to be classed as lyophilic. On passing a current 

 of 8 amperes under a head of 10 volts through cane juice contained in a 

 U-tube, there is a distinct migration of the colloids towards the anode, 

 the juice becoming clarified near the cathode. The colloids are hence 

 negatively charged. 



An observation well known in sugar-houses is the great increase in 

 the rapidity of filtration that takes place after the juices have become 

 alkahne. One of the major constituents of the defecation precipitate is 

 " cane wax," which, in turn, contains a large proportion of fatty acids. The 

 action of lime on these bodies will result in the formation of a soap, and 

 Kraffts^ has shown that in neutral solution such bodies behave as colloids, 

 becoming crystalloids in alkaline solution. Herein probably lies one, at 

 least, of the causes of this phenomenon. 



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