W. A. Davis 11 



the digestion was effected in the cold. Similarly, when the actual hot 

 digestion was carried out in the absence of basic lead acetate and the 

 latter was then added after cooling, the polarisation due to laevulose (or 

 dextrose) was not in the least interfered with. Le Docte concluded that, 

 as stated above, basic lead acetate should never be added to the hot 

 solution of sugars. 



Laevulose is far more sensitive to the action of basic lead acetate 

 in the cold than dextrose, just as it is far more easily decomposed, for 

 example, by acids^. The writer has found that dextrose and maltose 

 remain practically unchanged in presence of a considerable excess of 

 basic lead acetate and Le Docte {loc. cit.) also states that in presence 

 of dextrose only, the hot digestion with basic lead acetate can be carried 

 out without loss of reducing sugar. The fact that no loss of either 

 dextrose or maltose occurs in presence of basic lead acetate greatly 

 simplifies the analysis of solutions containing these substances. The 

 writer- has shown, for example, that basic lead acetate can be used in 

 removing impurities in the estimation of starch by means of taka- 

 diastase, without any loss whatever occm-ring of either of these sugars. 



In sugar analysis any large excess of basic lead acetate should 

 always be avoided and in most cases should be removed before taking 

 the actual polarisation readings, either by means of sulphurous acid, 

 as recommended by Pellet, or by sodium carbonate or sulphate. If 

 an excess of basic lead acetate is left it combines with the reducing 

 sugars (dextrose, laevulose and maltose) forming soluble lead com- 

 pounds which have an entirely different rotation from the sugars them- 

 selves. This is particularly the case with laevulose (or invert sugar) 

 the negative rotation of which may become positive in presence of 

 excess of basic lead acetate. In working with cane juices the experi- 

 ments of Watts and Tempany (loc. cit.) show that such slight excesses 

 of basic lead acetate as are ordinarily used in practice do not sensibly 

 interfere with the results. 



^ Davis and Daish, This Journal, 1914, 5, 454, 

 - This Journal, 1914, 6, 1.52. 



