DETERMINATION OF REDUCING SUGARS. 19 



This formula is that proposed by Tolman,* and is a modification 

 of the Clerget-Herzfeld formula. The factor .062B is the increased 

 reading to the left, due to the presence of 10 cc of hydrochloric acid 

 (specific gravity 1.20) in 110 cc of invert sugar solution. 



By the use of this formula it will be found that in the examinations 

 of many fruits and fruit products the apparent change in polarization 

 of a degree or two after inversion is not due to the presence of cane 

 sugar, but to the change brought about by the addition of the acid used 

 in inversion. It must be borne in mind that this formula is not appli- 

 cable in the presence of glucose, but is of special value in the accurate 

 determination of small amounts of cane sugar in fruits and fruit 

 products. 



Samples containing glucose may give results at least 1 per cent too 

 high, which will give an invert reading too low, owing to the action 

 of hydrochloric acid upon the maltose and dextrin. As will be seen 

 by reference to the tables, many of the glucose products show small 

 amounts of cane sugar (0.5 to 1.5 per cent), while, as a matter of fact, 

 this is an error due to the cause stated. 



BY COPPER REDUCTION. 



When only a small amount of cane sugar is present, it is best deter- 

 mined by calculation from the increase in reducing sugars after inver- 

 sion. For this purpose treat double the amount of fruit or fruit 

 product named under "Reducing sugars" with lead subacetate, and 

 after making up to volume and filtering, invert 50 cc in a 100 cc flask 

 with 5 cc of hydrochloric acid. After inversion neutralize the acid 

 with sodium hydroxid, precipitate the excess of lead with sodium sul- 

 phate, and dilute with water to 100 cc. Filter and dilute so that the 

 solution does not contain more than 1 per cent of reducing sugar. 

 The per cent of increase in reducing sugar after inversion multiplied 

 by 0.95 equals the per cent of cane sugar. 



DETERMINATION OF REDUCING SUGARS. 



Treat 5 grams of jelly (25 cc of a 20 per cent solution may be 

 employed) or other fruit product, or 25 grams of juice or fresh fruit, 

 with lead subacetate in excess (2 to 5 cc); make up to 100 cc and filter. 

 Transfer from 25 to 50 cc depending upon the percentage of reducing 

 sugar present to a 100 cc flask and add a saturated solution of sodium 

 sulphate in sufficient amount to precipitate the excess of lead; com- 

 plete the volume to 100 cc and use the filtered solution for the deter- 

 mination of reducing sugars. The approximate amount of reducing 



a Jour. Amer. Chem. Soc., 1902, 24, 515. 



