DEFECATIOX, PRINCIPLES OF. 291 



Settling Tanks. 



Besides the use of filters, for the removal of mechanical impurities, 

 the employment of settling tanks for the fresh juice, has been practiced 

 by some with excellent results. 



The only danger in this practice is, that fermentation is likely to 

 take place by letting the juice stand ; but this has been obviated bv 

 treatiugthe juice with sulphurous acid between tlie mill and the settling 

 tank. In this way it has been found practicable to keep the juice of 

 sugar-cane from 6 to 10 hours, and, upon standing, a large amount of 

 slimy sediment was separated from the juice. It is well to have the 

 juice drawn off from an inch or two above the bottom of the tank; the 

 sediments being reserved for vinegar, or passed througli the filter be- 

 fore it is added to the remainder of the juice. 



Effect of Heat on Juice. 



The juice, even after the most careful filtration, still retains many 

 impurities, which may by otiier means be removed. We have seen 

 that, in its natural state, it has an acid reaction due to the presence of 

 acid salts of organic acids, of the nature of which we as yet know little. 



There are also present certain nitrogenous matters, besides the inor- 

 ganic constituents or ash of the juice. The eilect of heat alone, is to 

 cause the coagulation of at least most of the nitrogenous matters, and 

 the formation of an abundant scum : and very many, seeing such quan- 

 tities of impurities removed by heat alone, are accustomed to relv upon 

 it solely in defecation. This is a serious error, although it must be ad- 

 mitted that excellent syrup, in appearance at least, has been made 

 without the use of any thing but the skimmer to remove those im- 

 purities which arose as the juice was being evaporated. Heat also, bv 

 destroying the germs, prevents or retards fermentation. Heat is a 

 valuable, but not a complete agent in the defecation of the juice. 



Effect of Lime on Juice. 



The agent which is almost universally employed in the defecation of 

 taccharine juices is lime, and, owing to its cheapness, general accessi- 

 bility, and the excellent results which attend its intelligent use, a de- 

 scription of its chemical properties, preparation, and use in defeca- 

 tion, is important. 



Lime belongs to the class of bodies known to the chemist as alkaline 

 earths, because, in its chemical nature, it appears to stand midway be- 

 tween the alkalies and the earths. Athough far less soluble iu water 

 than are the alkalies, it is yet sutfioieutly soluble to form a solution 

 pretty strongly alkaline in character, a clear colorless liquid, known as 



