15 



niparison of two methods for the determination of glycerol. 



THE DETERMINATION OF REDUCING SUOAXS is WINE. 



The foil. .win-.; criticism,! the provisional volumetric method of the association was 

 .n-.l l,\ 11 M Paul, Minn.: 



Tin- chin' ..l.jection to the present pn\ i.-i..ual methods for the determination of 

 reducing sugar* in win*- . liul. 107, p. 87) is the length of time necessary for the opera- 

 ti"ii tempi- have been made to remedy this defect by the introduction of 



Volumetric method-, \\hich as a rule have been unsatisfactory either through the 

 necessity i.f preliminar\ mm I.>H- or through the excessive errors caused by the 

 >l- 1-. >n<lit i"!i-> under \\ hich the copper i.- precipitated. It was decided after care- 

 ful ( on -i.it -ration that th*- actual precipitation of the copper by the provisional method 

 o>uld not l.e modified to a.l\ antaire. 1'iit that the ordinary methods of preparing the 

 sample, in addition to bi-ini; Imii: ami tedious in operation, are the sources of several 

 rore. A strong solution of alcohol fails to reduce Fehling solution, and, 

 such being the case, it is apparent that the addition of 25 cc of a 15 per cent solution 

 of ah c.hnl to l_'<) < . .f boiling diluted Kehlini: solution, from which it would be almost 

 immediately boiled off, could have little or no influence on the precipitation of the 

 copper. Since ihe pro\iM..nal nielli."! calls for the dealcoholization of the wine 

 previous to clarification, its omission would save at least a half hour without decreasing 

 the accuracy of the result. Furthermore, it has long been realized that the use of 

 lead subacetate as a clarifying ai^-nt has been attended with several errors. In the 

 tir.-t place, the precipitated soli.L- carry with them small amounts of sugar, and, in the 

 i taking an aliquot portion of the filtrate the volume of the precipitate 

 is not considered. This second error is repeated when the excess of lead is removed 

 with sodium sulphate, and all these errors together, when multiplied by the number 

 of times that the sample has been diluted during the preparation of the solution in 

 which the sugar is determined, may amount to a considerable proportion of the total 

 reducing sugar content of the wine. 



It is proposed, then, that the preliminary treatment of the wine consist of only the 

 dilution necessary to obtain a solution containing not more than 1 per cent of reducing 

 su-ar, that the copper be precipitated in the usual way, filtered as quickly as possible, 

 n -dissolved, and determined volumetrically or by electrolytic deposition. Analyses 

 were made on fourteen samples of wine by both the provisional and the proposed new 

 methods, with the results shown in the accompanying table. To make these results 

 more easily comparable, the sample was diluted with the same amount of water 

 for both determinations. 



