NOTE.* 



The Estimation of Natural Mixtures of Sugars. 



While going to press a paper on the estimation of the sugar 

 in apples was pubHshed by Evans ; f the method of analysis, 

 which is adapted to the accurate determination of sucrose, 

 fructose, and glucose, is as follows : 20 c.c. of the juice (ob- 

 tained by freezing the cut slices and expressing in a hand 

 press) were placed in a graduated flask, almost neutralized 

 with soda and diluted to 400 c.c. with distilled water ; 4 c.c. 

 of basic lead acetate were then added and the mixture allowed 

 to stand for ten minutes ; the excess of lead was thereupon 

 removed by the addition of an 18 per cent solution of potassium 

 oxalate and the mixture made up to 500 c.c. and subsequently 

 filtered. J 



The estimation of reducing sugars was carried out upon the 

 above filtrate, diluted to half strength, employing the method 

 of Lane and Eynon.§ 



The total sugars were estimated by adding to 100 c.c. of 

 the cleared solution, obtained as above, a sufficient quantity 

 of citric acid crystals to have 10 per cent of the crystalline 

 acid (CgHgO, + HgO) present ; the solution was then boiled for 

 ten minutes, cooled, neutralized with concentrated alkali, and 

 made up to 200 c.c, so that the dilution was the same as that 

 used for the determination of the reducing sugar. The re- 

 ducing power of this solution was then determined and the 

 difference between the total sugar and reducing sugar so 

 found was taken as the value for the sucrose present, ex- 

 pressed in terms of invert sugar. 



For the estimation of glucose and fructose the method of 

 Willstatter and Schudel || was employed. A quantity of sugar 

 solution containing approximately o-o8 gram of glucose was 



*From page 140, f Evans : " Ann. Bot.," 1928, 42, i. 



I According to a footnote attached to the paper subsequent work has 

 shown that this method of clearing entails a loss of sugar of the order of 

 3 per cent. 



§ Lane and Eynon : " J. Soc. Chem. Ind.," 1923. 42, 32- 



II Willstatter and Schudel : " Ber. deut. chem. Gesells.," 1918, 51, 780. 



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