114 MANUAL FOR SUGAR GROWERS. 



from the mill, before tempering, while others apply 

 it after tempering ; the author believes that it is used 

 to best advantage as late in the process of concen- 

 tration as possible, say after subsiding or just be- 

 fore the syrup is taken into the vacuum-pan. If 

 used early in the process there is danger of inver- 

 sion from the presence of the sulphuric acid gen- 

 erated, while if used before tempering a good deal 

 of the bleaching action is lost, as the solution must 

 be slightly acid to obtain a fine colour, and efficient 

 clarification cannot be obtained with acid juice. 



In making high-class sugars it is usual to " sub- 

 side," i.e., to allow the syrup, boiled to a density of 

 about 20 B., to stand for twelve hours, in order that 

 the impurities may settle to the bottom. Bright 

 juice, free from floating impurities, is thus obtained. 

 No fermentation or inversion takes place if the pro- 

 cess is properly conducted. 



Decolourisation of the juice is often effected by 

 forming a precipitate of some solid substance in the 

 juice. The carbonation and phosphoric-acid pro- 

 cesses may be taken as types of processes of this 

 class ; their success depends on the fact that precip- 

 itates tend to remove many kinds of vegetable col- 

 ouring matter from solution. 



In the carbonation process a quantity of lime far 

 in excess of that required to neutralise the juice is 

 added. This dissolves in the form of mono-sac- 

 charate of lime. Carbonic-acid gas is afterwards 

 forced into the solution, which decomposes the sac- 

 charate, with the formation of cane sugar and car- 

 bonate of lime ; the latter, being an insoluble sub- 



