32 



The custom among sugar chemists in the beet houses iii France and 

 Germany is to measure lOOcc. of juice in a flask graduated to 100 and 

 llOce., add lUcc. of a dilute solution of subacetate of lead, filter, and po- 

 larize; the increase in volume being corrected either by reading in a 

 liUOmm. tube or by addiugone tenth to the reading. I have found it more 

 advantageous, however, to take 50cc. of the juice, add lead, and make 

 the volume up to lOOcc. This gives a much more satisfactory liquid for 

 polarization, especially with impure juices, and the filtration is greatly 

 facilitated. The only object attained by using lOOcc. is the increase of 

 the reading and consequent lessening of errors of observation. This is 

 of but little importance, however, as 50cc. is three times the normal 

 quantity for most instruments. Even this objection may be done away 

 with by using a double length (400mm.) tube, providing the instrument 

 used will admit of the long tube, and this is entirely practicable so far 

 as the lucidity of the solution is concerned ; for I have never failed to 

 get clear, bright solutions by proceeding inlthe manner I have indicated, 

 except iii cases where juices had been allowed to stand and mucous fer- 

 mentation had set in. 



The detailed procedure is as follows : 



Fifty cubic centimeters of the juice is measured out by means of an 

 accurately calibrated pipette and run into a lOOcc. flask; to it is added 

 from 1 to 4cc. of a strong solution of sub acetate of lead, 1 the whole made 

 up to the mark with water, filtered, and polarized. 



The same solution is then used for the determination of the reducing 

 sugars by Fehling's solution, the excess of lead being precipitated by 

 sulphate of soda. As the reduction of copper sub-oxide by sugars has 

 been shown to be affected by the amount of dilution in which the action 

 takes place, it is desirable to have as nearly as possible a constant 

 amount of dilution, and the most favorable dilution is such that from 

 10 to 20cc. of the solution will be required to reduce the copper from lOcc. 

 of Fehling's solution; so, for juice presumed to contain from 1 to 2 per 

 cent, of reducing sugars, 50cc. of the solution, which has been polarized, 

 made up to lOOcc. will furnish the proper dilution ; for those containing 

 from 2 to 3 per cent., 50 to lOOcc., and so on. In the case of juices con- 

 taining less than 1 per cent, of reducing sugars the excess of lead may 

 be removed by adding the sodic sulphate 2 before the lead precipitate is 

 filtered off, when the same solution can be used for polarization and for 

 the reduciug-sugar determination. The copper solution used is Violette's 

 modification, and the operation is performed in large test-tubes from 9 

 to 10 inches long and of about 1 to l-inch caliber, and the end reac- 

 tion is obtained with ferrocyauide of potash and acetic acid, the small 



1 Prepared by rubbing up iu a mortar 1 kilo of acetate of lead and | kilo of litharge 

 aud boiling with | litre of water. 



2 YOT very exact work it is better to take a separate sample of the juice for the cop- 

 per test and dispense with the lead altogether if the purity of the juice admits, for 

 the presence of lead produces an error, aud even when precipitated by sulphate of 

 soda there is said to be an error from the slight solubility of the sulphate of lead. 



