THE DETERMINATION OF REDUCING SUGARS 



539 



white tile, and brought in contact with the indicator. The exact end-point 

 is thus obtained. Often it is well to make a preliminary test to obtain the 

 approximate result as a guide and to follow this by the analysis of record. 



A less convenient method of testing for the presence of unreduced 

 copper consists in filtering off a few drops of the liquid, acidifying with 

 acetic acid, and adding a drop of a solution of potassium ferrocyanide. 



The filtration from the suspended cuprous oxide may be made by using 

 very small filter papers folded into a cone and held in the liquid by a forceps. 

 The clear liquid will pass into the cone whence a drop may be removed by 

 means of a fountain pen filler. Alternatively, a Wiley^i filter tube may be 

 used. This consists of a glass tube, on the end of which a flange has been 

 formed. Over the flange is stretched a piece of linen, on which is formed 

 by suction an asbestos film. On applying suction to the tube a clear filtrate 

 passes through which can be tested with the indicator. Knorr^i modified 

 the Wiley tube by sealing in a platinum disc. 



Lingvo has prepared the following table giving the relation between 

 reducing power and concentration of the solution analysed : — 



The error due to the presence of cane sugar may be eliminated by the 

 use of the annexed tables, where column A gives the percentage of invert 

 sugar on total sugars present ; column B gives the percentage of invert 

 sugar as found by experiment, using the table immediately above ; column 

 C is B — A, which gives the error (due to the presence of cane sugar) in the 

 percentage of invert sugar so found. This table is referred to 0-2 gram of 

 invert sugar per 100 c.c. 



A. 



95-2 

 87 -o 

 80 -o 

 66 

 50 

 40 



33 



28 

 25-0 



22-3 



20 -o 

 13-8 



c. 



0-30 

 0-30 



0'35 

 0-26 

 o -24 

 0-25 

 o -24 



0-23 



o -14 



O -12 



o -10 



