THE DEFECATION OF CANE JUICE 



275 



limit however to a decrease in the number of units since time for settling 

 and decanting must be allowed, and the available time increases with the 

 number of tanks. For example, with four units each holding a half-hour's 

 supply from the mills, and with each tank taking the same time to decant, 

 only one hour's settling is possible. With eight tanks holding fifteen minutes' 

 supply each, the available time for settling is increased to ninety minutes. 

 In addition, an error in liming is more serious with the larger units, since it is 

 generally not detected till the tank has begun to settle. With eight tanks 

 it would be possible to cut out one tank for a round, but this could not be 

 done with only four in the circuit. 



The settling tanks / 

 should be made with 

 the bottoms inclined at 

 an angle of not less than 

 15 so that the deposit 

 may gravitate readily to 

 the discharge pipe. A 

 cylinder standing on a 

 cone forms a convenient 

 pattern. 



An advantage, how- 

 ever, in rectangular 

 tanks is that every two 

 tanks may have one 

 common side. A useful 

 accessory is the sight 

 glass indicated in Fig. 

 159, which allows the 

 rate of settling to be 

 observed. The clear 

 juice may be drawn off 

 by a series of cocks 

 located at different 

 levels, or by a float and 

 syphon discharge. This 

 system was introduced 

 by Sain thill in Jamaica 

 about 1770. Although 

 some heat is thereby FIG. 159 



lost, it is perhaps 



better to allow the clear juice to empty into a gutter rather than into a 

 closed pipe, as a better opportunity for inspection is afforded. 



Continuous Settling. In place of the intermittent system, continuous 

 arrangements have been installed in some factories. The form due to 

 Pickering and Macgregor, (patent 4834, 1901), is indicated in Fig. 160. The 

 juice enters at a, fills the annular space b, and flows upward at a very slow 

 velocity until it overflows into the gutter c, passing away at d. The dirt 

 at the same time settles on to the side of the cone e, from which it is removed 

 by the scraper /, eventually being discharged by the outlet g. When it is 

 necessary to clean the vessel, the clear juice in the cylinder can be run out by 

 the outlet h. 



