CANE SUGAR. 



Necessity to adhere to the same Conditions. The amount 

 of copper reduced by a weight of reducing sugar depends on the time of 

 boiling, the composition of the copper solution, the quantity used, and on the 

 concentration of the sugar solution ; and hence where accuracy is desired the 

 exact conditions under which the tables were constructed must be followed. 



General Considerations of Gravimetric Processes. 



The amount of copper reduced forms the basis of the calculation of the 

 corresponding amount of reducing sugars ; provided only cuprous oxide were 

 precipitated, weighings as cuprous oxide, as cupric oxide, as metallic copper, 

 or determination of the copper by other methods would give equivalent results. 

 In actual practice, and especially when dealing with low grade products, 

 equivalence is not found. Zerban and Naquin 9 , with pure invert sugar, 

 invariably found that the weight of cuprous oxide was greater than should 

 correspond with the weight of cupric oxide found after complete oxidation of the 

 former. They found, in addition, that the weight of cupric oxide corresponded 

 very closely with that of the copper determined in the precipitate, and this 

 difference they attribute to the retention of water by the cuprous oxide. 

 With actual factory products they found that the weight of both the cuprous 

 and cupric oxide was greater than that which corresponded to the copper in 

 the precipitate, and they attribute this to the co-precipitation of mineral 

 matter weighed along with the precipitate. It follows, then, that the excess 

 copper methods, to be considered accurate, demand the determination of the 

 copper in the precipitate, which can be done electrolytically, by the perman- 

 ganate or by the iodometric processes already given. In the writer's opinion, 

 this last process combines both convenience and accuracy. 



Direct Volumetric Methods. In these methods a fixed quantity 

 of alkaline copper tartrate solution is titrated with the solution under analysis 

 until all the copper is reduced. The copper solution is usually known as 

 Fehling's solution, and is of composition 



Copper sulphate, 34-64 grms. per 1000 c.c. 



Caustic soda, 80 grms., and potassium sodium tartrate, 180 grms. per 

 1000 c.c. 



Equal quantities of the above are mixed, and 20 c.c. of the mixed solution 

 are reduced by approximately '05 grm. glucose. 



As this method is the one usually employed in tropical sugar factories by 

 unskilled workers, it is described in full detail, the remarks and directions 

 applying mutatis mutandis to the other volumetric processes given. The mixed 

 solution of copper sulphate and alkaline tartrate is known as Fehling's 

 solution ; this is a deep blue solution which on boiling with glucose throws 

 down a precipitate of red oxide of copper (cuprous oxide), the solution at the 

 same time becoming lighter and eventually colourless, provided that a pure 



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