SULPHITATION 



291 



The purification due to the action of sulphur alone, however, does not 

 obtain in practice, since with the addition of lime to neutrahty a part of the 

 precipitate dissolves. 



Acid Waters in the Evaporation. — However carefully the acidity of the 

 juices is controlled, the condensed waters in the multiple effect will be found 

 to be acid, and to contain not only sulphurous but also sulphuric acid. 

 This is an evil which must be accepted, since, if an alkalinity sufficient to 

 prevent it were carried, the benefit of the application of sulphur would be 

 stultified. Hence when such waters are used as boiler feed, they must be 

 carefully neutrahzed with soda before going to the boilers. The most 

 efficient location to effect this neutralization is in the bodies of the vessels 

 themselves, thereby saving corrosion in the pumps and piping. This end is 

 obtained by allo^^ing carefully regulated quantities of soda solution to 

 flow into the vapour pipes or calandrias. The requisite quantity of soda as 

 carbonate should not exceed one lb. per 100 tons of cane. 



Sulpho-carbonation.^ — In this process, which is due to Harloff, and which 

 is known as the " acid thin -juice " process, the complete neutralization of 

 the first carbonated juice is effected by means of sulphurous acid. The 



,, — ^4.,.- 



'tt^mtt-ktritn' 



Fig. 171 



saturation may be carried out wholly by this acid or by a combination of 

 this and of carbon dioxide, the acidity finally obtained referred to phenol- 

 phthalein being from o-6 to o-8 c.c. normal per 100 c.c. By this means the 

 darkening of the juice on evaporation due to potassium carbonate alkalinity 

 is avoided, and there results a lemon-yellow sjTup affording a high-class 

 white sugar. 



Syrup Sulphitation.'^ — S}Tup sulphitation was introduced into Java bj- 

 Bach, and his process is in many ways the most rational one by which a 

 plantation white sugar can be made. The syrup as it leaves the evaporator 

 is treated with 2 to 2| per cent, of milk-of-lime at 15° Baiune equivalent 

 to from 0-3 to 0-4 per cent, of 6.xy lime. Immediately after the addition of 

 lime the material is sulphured to neutrality, and the copious precipitate 

 which is formed is filtered off. The clear filtrate is then sulphured to an 

 acidity of from 2 to 3 c.c. normal per 100 c.c. and boiled to massecuite. 

 SjTup filtration may, of course, be combined with any of the other routines, 

 and is to be recommended as the surest means of giving a material free from 

 suspended matter, upon which the brightness of the sugar largely depends. 



Apparatus used in Sulphitation. — In the apparatus employed in sulphuring 

 there are two independent units, the oven and the absorption appliance. 

 The oven is merely a cast-iron chamber into which the sulphur is introduced 



