Sugar 



109 



Purification of the Juice. The juice of the beetroot as it leaves the diffusion battery is a 

 turbid liquid of a deep purple or violet colour, with a peculiar taste and smell. As in the case 

 of sugar-cane raw juice it contains two groups of impurities : (1) those which are solid and can 

 be removed by filtering, (2) those which are in solution and accordingly cannot be got rid 

 of by filtering until they have been rendered insoluble by appropriate chemical methods. 

 The proportion of sucrose in the two liquids is about the same, some fourteen to fifteen 

 per cent, but in the beet juice there is a higher percentage of impurities to be got 

 rid of. 



Defecation with lime was the first method employed. This has already been described 

 and need not be more than referred to here. It has been generally abandoned as a good 

 method of purifying beet juice. Other means were also adopted but have all given place to- 

 what is known as " carbonatation." It was the discovery of the carbonatation process which 

 rendered possible the use of diffusion, because defecation with lime, although successful with 

 the juice obtained by rasping and pressing beetroots, was not found useful with the juice 

 resulting from the diffusion process. The process usually employed now is that, known as 

 double carbonatation. The juice is treated with an excess of lime and heated as in ordinary 

 defecation. Carbonic acid gas, generated by roasting chalk or limestone in kilns, is passed into 

 the liquid, combines with the excess of lime to re-form chalk which, being insoluble, renders the 

 liquid cloudy, and afterwards settles as a deposit. Too much carbonic acid gas, however, 

 must not be added or another compound is formed which is soluble again, and undoes the good 

 already accomplished. At the proper moment, therefore, the introduction of carbonic acid 

 gas is stopped, the chalk, etc., allowed to settle, and the clear liquid drawn off, and, if necessary, 

 filtered. The juice is now again treated with carbonic acid gas. It is kept hot during 

 the carbonatation processes and also heated again previous to being filtered. 



The syrup is forced through filters under a certain pressure, when it leaves behind the 

 so-called purifying scum, which forms flat cakes between the sieves of the filters. Afterwards 

 these cakes fall into a separate pit and are used as manure. 



Although the syrup is fairly consistent when it has been filtered, it does not contain a 

 sufficiently high percentage of sugar ; there is too much water in it, and concentration is 

 necessary. A peculiar machine is used for the purpose, characteristically called " appareil d 

 triple effet," or more generally known as a " triple effect," the principle of which has already 

 been explained under sugar-cane manufacture. It consists essentially of three kettles, 

 which can be heated at low pressure, and through which the liquor successively flows, 

 evaporating more and more. 



Boiling. Beetroot juice 

 contains comparatively 

 speaking large quantities of 

 mineral substances, or ash, 

 in solution. These are not 

 all removed by the carbona- 

 tation process, but as the 

 liquor is evaporated in the 

 triple effect and the water is 

 got rid of they are thrown 

 out of solution simply be- 

 cause enough water is no 

 longer present to dissolve 

 them. Before the final pro- 

 cess of concentration in the 

 vacuum pan can be proceeded making sugar loaves 



