178 PREPARATION OF FARINA AND SUGAR. [VII. 



relations. The use of both an acid and an alkali are therefore 

 required for effectual defecation. 



The freshly-rasped pulp is to be mixed with ^^-q of its 

 weight of sulphuric acid. All oxidation (?) is thus prevented 

 and the quantity of juice increased, while the pulp retains its 

 whiteness. Three per cent, of plastic clay is added to the 

 juice to remove its cloudiness, and at the end of twelve hours 

 separated by filtration. The filtrate, which runs through per- 

 fectly limpid, is entirely proof against viscous fermentation, 

 but still contains foreign matters, which are to be removed by 

 the usual process of heating with milk of lime. The juice, 

 thus defecated, yields by evaporation and crystallization, a 

 very fair sugar without the use of boneblack. 



Phosphoric would be preferable to sulphuric acid, were it 

 less costly. The use of the latter is attended with several 

 serious disadvantages ; one of which is the difficulty in re- 

 moving the sulphate of lime formed, and another in preventing 

 injury to the juice at the temperature 167° F. required for 

 its rapid filtration. Both of these might probably be obviated 

 by the substitution of phosphoric acid. See details in Lond. 

 Journ. xxxvi. 403. 



Sugar-filters. — For filtering saccharine and other liquids, a 

 patent appears in the Lond. Journ. xxxvi. 107, in which a 

 cycle of filters is used, the bottom of each being connected 

 by a pipe with the top of the next. The first liquor is run 

 into that one longest in use, and passes successively through 

 the others. One is always out of use, and being prepared 

 with a fresh charge of boneblack. 



A filter of cotton for sugar solutions is described in Lond. 

 Journ. 1849. About 2ilfe of raw cotton are drenched with 

 hot water and allowed to remain in water for 12 hours. A 

 little chalk and starch, with a boiling heat and skimming, are 

 used to remove a portion of the impurities. The drenched 

 cotton is then put on the slat-bottom of a cylinder or conical 

 filter and a little water poured through, which is run off by a 

 cock under the false bottom. The sugar solution is next 

 .poured on the filter, and, after passing through, is immediately 



