November, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



269 



of rollers. The bagfasse is dried and used as fuel, be- 

 cause in most places where sug'ar cane is manufactured 

 fuel is expensive and difficult to- obtain. 



The juice, as it comes from the presses, is sometimes 

 an opaque straw-yellow coloured fluid, but is often of a 

 greyish-ifreen. It usually contains a considerable 

 quantity of suspended matter, which requires to be 



(.J— Incrustation of wax on epidermis, 

 Fig. 2. 



lagnificd. Z>— Floret.] 



separated, such as fibres from the cane, albuminous 

 matter, sand, and clay, etc. Owing-, however, tO' its 

 slimy nature, filtration is by no means easy. 



In order, therefore, to clarify the juice, it is treated 

 with lime. There are two processes of liming-, defeca- 

 tion — in which only a small quantity of lime is em- 

 ployed — and carbonation, where an excess is added, 

 and afterwards removed by passing in carbonic acid 

 g-as. The addition of the lime neutralises the free acids 

 in the juice, thus preventing inversion, i.e., conversion 

 of the saccharose into glucose, when it is subsequently 

 heated, and it also combines with the albumen. .A.ll 

 these insoluble materials enclose the solid impurities 

 already in the juice, and carry them down as they are 

 precipitated. 



Before adding lime, the juice is heated in steam- 

 jacketed pans to about 80°. Milk of lime is now added 

 in the requisite quantities, the mixture is then brought 

 to the boil, when a scum which contains many of the 

 impurities, rises to the surface, and is skimmed off. 

 The middle layer of the juice is found tO' be quite clean, 

 the upper layer is turbid, and the lower layer contains 

 the main portion of the precipitated matter. The 

 three layers are drawn off separately, the upper and 

 lower ones being passed through filter presses. 



The defecated juice is now ready for concentration. 

 The old and wasteful method was to heat the juice in 

 a series of pans over an open fire. This was wasteful, 

 because of the large amount of fuel required, and be- 

 cause of the possibilities of burning the syrup. 



The syrup to-day is, almost invariably, evaporated 



in vacuum pans ; the syrup from the beet always. '1 he 

 amount of fuel used in France, with the old, open-fire 

 method, for 1 ,ooolbs of beets, was 40olbs., to-day, less 

 than loolbs. of fuel is required. The most modern and 

 satisfactory system of evaporation in vacuum is known 

 as the multiple effect, it was invented by the Franco- 

 American Rillieux. The system is shown in Fig. 4. It 

 consists of three evaporating pans, C, C, C, the con- 

 denser D, and the pump P. Steam at about 7lbs. pres- 

 sure is let into the heating tubes of the pan furthest 

 away from the pump — the tubes are covered with the 

 syrup to be evaporated. The steam causes the sug-ar 

 solution to boil. Owing to the vigorous boiling, and 

 noco«densation, there is not xery much vacuum in this 

 pan, but the steam from the evaporation passes into 

 the heating system of the next pan, where there is a 

 greater vacuum, therefore, the juice boils at a lower 

 temperature. The steam from this pan now passes 

 into the heating: system of the last pan, which is under 

 a very considerable vacuum, consequently, the juice 

 boils at a much lower temperature, and the steam from 

 it is continually condensed by passing into a well cooled 

 condenser. All the pans are connected together by 

 cocks, so that the juice can be run from one pan to the 

 other. During the evaporation this is done continu- 

 ously. 



When the juice is sufficiently concentrated, it is 

 pumped out of the last pan. During the evaporation 

 many substances held in solution by the clarified juice 

 separate out, so that the juice becomes turbid again. 

 It is very important to remove these impurities, be- 

 cause they become enclosed in the sugar crystals during 

 the subsequent boiling process. The juice does not 

 filter well, so is usually purified by boiling the syrup in 

 eliminating pans, and treating with caustic soda or 

 sulphurous or phosphoric acid, as may be found 

 necessary. 



The next process is the boiling, or final concentra- 

 tion of the syrup. This is usually done in single 

 exaporating pans. The .syrup is drawn into the pan, 

 which is generally of iron, and contains coils for heat- 

 ing purposes. The boiler requires toi be a man of great 

 experience, because the yield and grain of the crystal- 



lised sugar depends entirely upon manipulation. It is 

 not easy to explain shortly the manner in which this 

 important process is carried out. For obtaining a 

 sugar of averag-e size grain, the procedure is essentially 

 as follows : The syrup is drawn into the pan, which is 

 under a vacuum of about 24 inches, the boiling point 

 will then be about 60° (140° Fahr.). Steam is gradually 



