180 



Summing up the work, it can be said that where reducing sugar determinations 

 follow polarizations the clarifying agent should be neutral lead acetate. But for 

 ordinary polarization work, where the reducing sugar content is not high, either sub- 

 acetate or neutral acetate can be used. Where the content of invert sugar is high, a 

 double polarization is necessary to obtain the correct figure for sucrose, and then any 

 of the clarifying agents can be used, but care should be taken not to use an excess. 



There is one point to which special attention should be called, namely, the 

 estimation ofreducing sugars. In Bulletin 107, Revised, page 53, under 6, Direct 

 Weighing of Cuprous Oxid, the weighing as cuprous oxid will give too high results if 

 the material under examination is high in nitrogenous matter or mineral salts; xanthin 

 bases and some other nitrogenous bodies are thrown down by the Fehling solution 

 along with the cuprous oxid. Also some baits are precipitated, and would be weighed 

 as cuprous oxid, thereby giving false results. This has been conclusively shown by 

 C. A. Browne in his reports as referee on sugar for the past two years, and is borne out 

 in all of the referee's work. In such cases the copper of the precipitate must be de- 

 termined direct either as cupric oxid or, better, by some volumetric method, as Low's, 

 where the cuprous oxid is dissolved, treated, and finally the copper estimated by 

 titration with thiosulphate. This is a longer procedure than the weighing as red oxid, 

 but it should be done if reliable and accurate figures are to be obtained. 



RECOMMENDATIONS ON SUGAR. 



It is recommended 



(1) That the question of the influence of precipitants upon the polarization of sugars 

 be further investigated. 



(2) That the question of methods of determining moisture or dry substance be 

 further investigated. 



(3) That the method of determining dry substance by means of the refractometer 

 and the table of Geerligs be adopted provisionally by the association. 



(4) That under "Methods for the Determination of Copper contained in the Pre- 

 cipitate of Cuprous Oxid," pages 51-53, Official Methods, Bulletin 107, Revised (6) 

 "Direct Weighing of Cuprous Oxid," there be a limitation inserted, viz: "This method 

 should not be used in determining reducing sugars in commercial products, as other 

 substances are precipitated along with the cuprous oxid. In these products the 

 copper of the cuprous oxid should be determined direct by titration as in Low's 

 method (ibid., 241) or as cupric oxid." 



DETECTION OF SMALL PERCENTAGES OF COMMERCIAL GLUCOSE 

 IN SIRUPS AND HONEY. 



By A. H. BRYAN, Referee. 



The provisional method of this association is the one described on page 70 of Bulletin 

 107, Revised. It calls for a polarization of the inverted solution at 87 C. A dextro- 

 rotary reading at this temperature is said to be due to commercial glucose. And to 

 obtain the percentage of glucose, the method divides this reading by the factor 163 

 and multiplies by 100. 



C. A. Browne, in his report on honey, Bulletin 110, shows that normal honey 

 naturally has a dextrorotation at 87 C. and hence the results of a determination by this 

 method would not express the truth. The dextrorotation of a honey is due to honey 

 dextrins. These are of a different character from those obtained by acid hydrolysis of 

 starch, or such as occur in commercial glucose. One point of difference is the fact that 

 honey dextrin is not colored by iodin solution, while the dextrins of glucose, except in 

 cases of a high conversion product, are colored by iodin. By means of this test, Beck- 



