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 21 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 21 modified 

 the Wiley tube by sealing in a platinum disc. 



Ling 20 has prepared the following table giving the relation between 

 reducing power and concentration of the solution analysed : - 



C. C. Fehling's 

 solution used. 



21 



22 



23 



24 



25 



26 



27 



28 



29 



3 



31 



Invert Sugar 

 in 100 c.c. 

 o -2411 

 o -2311 

 o -2218 

 o -2132 

 o -2052 

 o -1980 

 o -1910 

 0-1846 

 0-1787 

 0-1731 

 0-1678 



C. C. Fehling' 

 solution used. 



32 



33 



34 



35 



36 



37 



38 



39 



40 



41 

 42 



Invert Sugar 

 in 100 c.c. 

 o -1629 

 0-1583 



0-1539 

 0-1497 

 0-1458 

 o -1421 



0-1385 

 0-1349 

 0-1319 

 o -1288 



0-1259 



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 

 66-7 

 50 -o 

 40 -o 



33-4 

 28-6 

 25 -o 



22-3 

 20 -O 



13-8 



B. 



95'3 

 87-1 

 80 -i 

 66-9 

 50-4 

 40-4 



33-8 

 29 -o 



25-4 



22-7 

 20-4 



14 -10 



C. 



O ! 

 O -I 



O -I 



O -2 



0-4 

 0-4 

 0-4 

 0-4 

 0-4 

 0-4 

 0-4 

 0-3 



A. 



ii -8 



10-3 

 9-1 



7-5 

 6-2 



3'9 



2-8 

 2 -O 

 I -O 



0-8 

 0-7 



B. 



12 -IO 

 10 -60 



9-45 

 7.76 

 6-44 

 4*5 

 3'4 

 2-23 

 i -14 

 o -92 

 0-80 



C. 



o *3 

 o '30 



o-35 

 o -26 

 o -24 

 o -25 



0-24 

 0-23 

 0-14 



O -12 

 O -IO 



