COXCEXTRATIOX OR EVAPOEATION OF JTJICE. 325 



CHAPTER X. 



(a.) Concentration or evaporation of juice. 



(6.) Methods of evaporation. 



(c.) Vacuum pans. 



(d.) Multiple effects. 



(e.) Separation of sugar from molasses. 



(f.) Sucrates of lime and strontia. 



CONCENTRATION OR EVAPORATION OF JdCE, 



Having, by filtering and defecation, separated as far as possible the 

 impurities of the juice, the next step in the production of sugar is the 

 removal of the excess of water, which is always present in saccharine 

 juices. 



By reference to the table on page 336, it will be seen that a solution 

 of sugar, boiling at a temperature of 239° F. (115° C), for example, 

 -will contain 85.2 per cent of sugar and 14.8 per cent of water, and 

 if this solution is allowed to cool down to 60° F. (15.5° C), the water 

 present will hold in solution about twice its weight in sugar; i. e., the 

 14.8 parts of watei will dissolve 29.H parts of sugar, and the re- 

 maining portion of sugar, 55.6 parts, will crystallize out from the so- 

 lution. As the temperature is increased, the amount of water neces- 

 sary to dissolve a given weight of sugar becomes less, as will be seen 

 by consulting the table on page 336. 



In slowly passing from a state of solution to that of a solid, those 

 bodies, as sugar, salt, and others, which are able to assume a crystal- 

 lizable form do so. 



From the composition of the juice, it wQl be seen that about 84 per 

 cent is water; i. e., the sugar in the juice is in a solution of about five 

 times its weight of water, and a large proportion must be removed in 

 order to secure this sugar. 



In order that this matter, which is fundamental, may be thoroughlv 

 understood, a few illustrations of the principles involved are given. 



Common salt is soluble in about three times its weight of water. 

 Suppose, now, that a pound of salt is dissolved in three pounds of 

 water, and we evaporate rapidly one and a half pounds of water from 

 the solution, it will be found that about half a pound of the salt will 

 be thrown down as a solid, but in a fine powder. If, however, the 

 water is slowly evaporated, we will have the salt crystallizing out in 

 large cubical crystals. 



