ESTIMATION OF CARBOHYDRATES 



Caven and Hill's Method. 



Caven and Hill in 1897 and 1898 suggested that the cuprous oxide should 

 be dissolved in an acid solution of permanganate (i part H 2 SO 4 , 3 parts H 2 O 

 and *2N KMnO 4 standardised against oxalic acid) and the titration of the 

 permanganate used in the oxidation with oxalic acid. In the actual process 

 it was preferred to add excess of oxalic acid and to titrate back with per- 

 manganate. 



The amount of cuprous oxide was obtained by multiplying the oxygen 



value of the permanganate by 8*91 ( i ) and the glucose by using the 

 factor '5045. 



Sidersky's Method. 



This method has been used by sugar experts chiefly in France. The 

 cuprous oxide is dissolved in excess of standard sulphuric acid and the excess 

 determined by titrating, with ^N ammonia. It is carried out as follows : 



The cuprous oxide is filtered off and washed free from alkali. It is 

 dissolved in 25 c.c. N sulphuric acid, a few crystals of potassium chlorate 

 being added and the reagent heated till solution is effected. An equivalent 

 quantity of standard ammonia is added; a blue colour is obtained and 

 N sulphuric acid is run in till the colour is of a permanent greenish tint. 

 The copper sulphate is thus the indicator. 



The amount of glucose is calculated as follows : 

 i c.c. N H 2 SO 4 ss -0318 gm. copper. 



The amount of invert sugar is given by multiplying by '3546. 



II. (b) (ii) Estimation of Residual Cupric Salt. 



Numerous suggestions have been put forward for estimating the excess of 

 copper sulphate which is not converted into cuprous oxide by reduction by 

 glucose : thus 



(1) Weill and also Pellet suggested its titration with zinc chloride. 



(2) Maumene suggested its titration with sodium sulphide. 



(3) Lehmann in 1897, Riegler in 1898, Maquenne in 1899, and Schoorl 

 in 1899 suggested its titration with potassium iodide and thiosulphate. 



(4) Volhard suggested its reduction with sulphur dioxide and precipita- 

 tion as cuprous thiocyanate with excess of ammonium thiocyanate, and the 

 estimation of the thiocyanate with silver solution. 



(5) Bang suggested its titration with hydroxylamine. 



Of these methods that of Lehmann or Maquenne and of Bang are the 

 simplest and are frequently used. 



