Messrs Wood and Berry, A rapid method of estimating sugar. 97 



A rapid method of estimating sugar. By T. B. Wood, M.A., 

 Reader in Agriculture, and R. A. Berry. 



[Read 2 March 1903.] 



The work described in the following paper necessitated a large 

 number of determinations of sugar in the juice of swedes. The 

 mixture of sugars in swedes is such that polarimetric estimation is 

 not available. A rapid and fairly accurate titrimetric method 

 had therefore to be devised. After many trials the following 

 method was found to be very satisfactory. The juice, after being 

 clarified with basic lead acetate, treated with dilute acid to invert 

 the cane sugar, and neutralized, was diluted until it contained 

 between - 5 and 1*0 per cent, of reducing sugar. The copper 

 solution used was made by dissolving 235 gms. of copper sulphate, 

 250 gms. of potassium carbonate, and 100 gms. of potassium 

 bicarbonate in 1 litre. This solution was tirst suggested by 

 Soldaini, Gaz. Ghim. Ital. 6. 322, and Ost (Ber. d. d. Ghem. Ges. 

 24. 14. 3003) has pointed out its many advantages over Fehling's 

 solution and worked out a table giving the relation of sugar 

 present to copper reduced for varying strengths of solution. The 

 advantages are that it keeps much better than Fehling's solution, 

 that it has much less action on cane and similar non-reducing 

 sugars and other substances likely to be present in plant juices, 

 and that a given weight of sugar reduces nearly twice as much 

 copper as it does from Fehling's solution. 



The only disadvantage is the necessity for rather long boiling 

 to get constant results. 



To 50 c.c. of the copper solution already boiling, 10 c.c. of the 

 sugar solution are added, and the boiling kept up for 10 minutes. 

 The cuprous oxide is then filtered off on asbestos felt in a Gooch's 

 crucible and washed with boiling water. It is then transferred 

 to a wide-mouthed stoppered bottle already filled with carbon 

 dioxide. The last traces are washed through the Gooch with 

 25 c.c. of 2-L°/ ferric sulphate solution in 25 per cent, sulphuric 

 acid, and the stopper put in the bottle. A few seconds' shaking 

 at once causes the cuprous oxide to dissolve, reducing an equiva- 

 lent amount of ferric sulphate to ferrous. This is then titrated 

 with standard solution of potassium permanganate of such 

 strength that 1 c.c. oxidises the ferrous salt formed by the 



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