1918] CURRENT LITERATURE 181 
destroyed by boiling, the residuum is filtered, washed, the solution made to 
volume, precipitated with lead, using care to avoid an excess, and portions are 
taken for polarization and for reduction. Values for the maltose-dextrose 
mixture are then calculated from the tables of BRown, Morris, and MILrar. 
Datsus has determined the cupric reducing power of xylose and arabinose 
under the standard conditions prescribed by Brown, Morris, and MIL1ar, 
as all previously published values were determined under somewhat different 
conditions. He presents tables of the reducing power of each of these sugars 
for quantities between 10 and 200 mgm. Two curves obtained by plotting the 
reducing power, expressed as CuO, against the weight of sugar employed are 
given; from these curves it is possible to determine the weight of sugar corre- 
sponding to any given weight of CuO by the employment of a divisor number 
The reducing powers of xylose and arabinose are almost identical and differ 
very little from that of dextrose; thus for roo mgm. of sugar the divisor number 
for dextrose is 2.358, for arabinose 2.536, and for xylose 2.490. 
Davis and SAwvER* have presented evidence that free pentoses are quite 
generally present in the alcoholic extracts of plant material. This evidence 
they summarize; there are present substances which are soluble in 80 per cent 
alcohol, which are not precipitable by basic lead acetate, which are not ferment- 
able by ordinary yeasts, and which give the solution reducing power after all 
fermentable sugars have been destroyed by yeast. This reducing power, if 
calculated as that of a mixture of xylose and arabinose, agrees almost exactly 
with the pentose value of the phloroglucide obtained by a KrOBER-TOLLENS 
distillation of the solution after previous precipitation with basic lead acetate. 
se facts can only be explained upon the assumption that the furfural 
obtained in distillation is derived from free pentoses, not from pentosans, 
gums, or other sugars. 
Various plants, as marigold, turnip, carrot, potato, Helianthus, and 
Tropaeolum, showed the presence in the leaves of pentoses in amounts ranging 
from 0.3 to 1.0 per cent of the total vacuum-dried material, when determina- 
tions were made by the Kr6Ber-ToLLens method pani prepared 
su 
Sugar, in the solution to be distilled gives results which are opacity above 
the true pentose content. Consequently it is necessary, when very accurate 
determinations of pentoses are desired, to remove the other sugars by ferment- 
ing with Saccharomyces cerevisiae and to make the determination by distillation 
of the fermented solution. 
Datsn, ArtHUR JouN, Methods of estimation of a be The 
cupric reducing power of the pentoses xylose and arabinose. Jour. Agric. Sci. 6: 
es 1914. ‘ 
vis, Witt1am A., and Sawyer, GeorceE CoNnwortH, The estimation of 
Pr owes IV. The presence of free pentoses in plant extracts and the influence 
of other sugars on their estimation. Jour. Agric. Sci. 6:406-412. 1914. 
