272 



CHAPTER XIV 



number of c.c. necessary to make 100 c.c. of juice alkaline to phenolplithalein 

 determined for each tank, using the method described in the previous chapter. 

 If a lime-cream of strength 5 normal be used, then as many measuring 

 vessels as c.c. used in the testing would make the juice just alkaline to 

 phenolphthalein. All commercial limes are more or less impure, and it so 

 happened that, in one case when working as above, and using the actual 

 number of measuring vessels as indicated by the test, the desired aci- 

 dity was obtciined. The testing was done at the liming tanks, and, as each 

 tank took six minutes to fill, there was ample time to make the test with due 



care. The chief difficulty was experienced 

 in keeping the lime-cream at a uniform 

 density. This source of trouble can be 

 avoided by using two lime-cream agitators, 

 each holding about two hours' supply 

 of lime-cream. One container is prepared 

 and kept weU agitated by mechanical 



^ n n n fl tl H fl fl'il^-S W PTH h n^^^i^S > ^^^ attendant has then ample 

 I 'iWlri I — I r time to prepare the second tank while 



the first is emptjdng. A 5-normal lime- 

 cream is of density 15° Baume, and, if 

 this is thought to be too heavy, a 2-5 

 normal lime-cream mixture may be used, 

 the other solutions and containers being 

 altered to correspond. 



The writer does not favour the use of 

 automatic liming devices, since consider- 

 able variation in acidity occurs from tank 

 to tank, for which no automatic device 

 can make allowance. 



A difficulty in operation of this scheme, 



and indeed of any scheme, occurs in this 



process in connection with the filtration 



of the scun s. In order to obtain a rapid 



^ I I filtration it is necessary to lime the scums 



tqJ IIUUul-lHMyMMH >-^ =J\ to very distinct alkalinity. If this very 



alkahne filtrate be then mixed with the 

 clear defecated juice, a disturbance in the 

 system obtains together with a second 

 precipitation in the clear juice. To avoid 

 this, the alkahne filtrate may be syste- 

 matically returned to the raw juice (after 

 the latter has been weighed or measured), 

 when the excess of lime is neutralized, the control of the additional lime 

 cream required being made as before. By the use of this method a clear 

 defecated juice is obtained with a minimum of lime, and, at the same time,^ 

 the advantages of the rapid filtration of the scums are retained. 



The Practice of Defecation. — After the juice has received the proper 

 quantity of lime, it is necessary to raise its temperature to a minimum 

 of igo° F. in order to obtain a rapid setthng and separation of the precipitate. 

 The heating is done either in tubular heaters or in the tanks, which serve as. 

 containers for the juice, or in a combination of these two apparatus. 



Fig. 155 



