THE DEFECATION OF CANE JUICE 



It must have been observed b\^ anyone who has operated a cane sugar 

 house that great variations occur in the rate of setthng, and in the vohime 

 occupied by the mud. Prima facie these variations may be attributed to 

 variation in the reaction of the juice as regards alkahnity and acidity, or, in 

 other words, to the quantity of lime used. Accordingly, a juice which 

 had an acidity of 1-75 c.c. normal per 100 c.c. (c/. Chapter XIII) was luned 

 with 2 • o, 1-75, I • 5, I • 25, 1 • o, o • 75 and o • 50 c.c. of normal lime suspension 

 per 100 c.c. of juice. The juices so treated were then heated to the boiling 

 point, boiled for one minute under a reflux condenser, poured into a tube one 

 metre long round which steam circulates, and allowed to settle. The results 

 obtained are tabulated below, the figures giving the depth of the clear 

 supernatant column of juice in millimetres. The approximate position of 

 the critical position is indicated by an asterisk. 



C.C. Normal Lime per 100 c.c. of Juice. 



30 843 863 873 880 



Of these juices the two with the lowest quantity of Ume were " muddy " 

 and distinctly underlimed ; the next in order was fairly bright, while the 

 two following ones were bright and clear and could be taken as representative 

 of satisfactory defecation. The two remaining juices, while quite bright and 

 clear, were distinctly overlimed. 



A very great difference may be observed in the rate of settling, and also 

 in the ultimate volume occupied b}' the mud. In addition, the method of 

 separation of the precipitate was different, the two juices with least lime 

 affording a mud that separated in large " flocks," while in the others the pre- 

 cipitate was evenly distributed at the beginning of settling. Correlat- 

 ing this experiment mth those described in Chapter XIII, an acidit}^ in the 

 juice referred to phenolphthalein of from 0-25 to o • 50 c.c. normal per 100 c.c. 

 of juice would appear to fulfil all the conditions demanded for a good defeca* 

 tion, i.e., protection against inversion, a bright and clear juice and reasonably 

 rapid settling. It is true that the maximum purification is only obtained 

 when the juice just reaches alkalinity, but the advantages obtained by the 

 use of less lime are to the writer's mind of more moment. 



Determination of the Quantity of Lime required. — A method pursued by 

 the writer in a certain factory was as follows : — An acidity of 0-5 c.c. normal 

 per 100 c.c. juice was selected as standard. Lime-cream measuring vessels 

 were prepared of volume one- thousandth that of the tanks in which the juice 

 was received. A half-normal solution of caustic soda was prepared, and the 



