May 3 , m 4 Modifications of the Picric Add Method for Sugars 
485 
4 ‘reducing ’ 1 sugars was used; the effect of heating these various sugars with 
picric acid was not determined. The values given in Table V are for anhydrous 
sugars, and are based on glucose as unity. They are the ratios of the color 
intensity of glucose compared to the intensities of equal weights of the other 
.sugars. 
Table V. —Color values of various sugars , compared with glucose as 1.000 
Sugar 
Color 
value 
Conversion 
factor 
Sugar 
Color 
value 
Conversion 
factor 
Glucose 
1.000 
1.000 
0.770 
1.000 
0.883 
1.000 
1.000 
1.298 
1.000 
1.132 
Rhamnose. 
1.298 
0.750 
1.000 
1.071 
0.774 
1 .333 
1.000 
0.934 
'Fmetose _ _ 
Lactose.. 
TVfftJfcnsft 
Arabinose__ 
Mannflsft 
Xylose..... 
Galactose_ 
Fig. 2.—Curves showing the differences in color value obtained when the standard is set at 10, 20, 30, 40, 
and 50 mm. 
In using this method on solutions of sugars other than those having a color 
value of 1.000, either a standard may be made from the pure sugar involved, or 
the ordinary glucose standard may be used; and, after calculating the sugar 
content in the usual manner according to the suggestions below, the number 
obtained is multiplied by the conversion factor given in the table for the particular 
sugar involved. 
MINOR PRECAUTIONS 
Rhode and Sweeney {15) and Benedict ( 1) have emphasized the importance 
of the purity of the picric acid used in this method, not only from the standpoint 
of its color-producing properties, but from that of its precipitating power towards 
proteins. The writers tried the various methods of purification of picric acid 
that have been suggested, and found practically no difference. Therefore 
simple recrystallization from hot water acidified with 15 cc. of concentrated 
hydrochloric acid per liter is recommended. 
Benedict and Osterberg {2) pointed out the necessity of a proper proportion of 
picric acid to sugar. The writers found that varying the proportions does affect 
the intensity of color produced. They therefore emphasize the necessity of using 
