May 3 ,1924 Modifications of the Picric Acid Method for Sugars 487 
COLOR MEASUREMENT 
The zero point of the colorimeter is adjusted, using the standard color solution 
on both sides. The reducing and total colors are measured against the standard 
set at 30 mm. or at 20 mm. 
CALCULATION 
R =/ r x Std. 
T =f t x Std. 
S =0.95 (T-R). 
T 1 —R-\-S 
Where 
R =per cent of reducing sugars in the solutions analyzed. 
S =per cent of sucrose in the solution analyzed. 
T =per cent of total sugars (apparent) in the solution analyzed. 
T' —per cent of total sugars (true) in the solution analyzed. 
/ r =the factor obtained from Table IV, corresponding to the colorimeter 
reading for the reducing sugars, and to the position of the standard 
(30 or 20 mm.) for reducing sugars. 
ft =the factor obtained from Table IV, corresponding to the colorimeter 
reading for the total sugar and to the position of the standard (30 or 
20 mm.) for the total sugar. 
Std. = value of the standard in terms of per cent of glucose. 
SUMMARY 
1. A search for a reasonably permanent color standard for use with the picric 
acid method for sugars has been unsuccessful. The best standard is either an 
0.08 per cent glucose solution, or an 0.076 per cent sucrose solution, in saturated 
picric acid, which will keep for about a week; or these same solutions in water, 
in which case they must be used at once. 
2. Heating glucose in a solution of picric acid previous to reduction in a sodium 
carbonate solution gives a greater color value than without the treatment. 
3. When the picramate color is diluted, the intensity of the color is not pro¬ 
portional to the dilution. Therefore the color is always diluted to exactly 10 cc. 
4. Clarification of sugar solutions has proved to be unnecessary in a number of 
cases when the picramate method was used. 
5. The intensity of the picramate color is not proportional to the amount of 
sugar present. Therefore a table has been compiled which gives factors to be 
used throughout the range of colorimeter readings. 
6. The color values for 8 reducing sugars, in comparison with glucose, have 
been determined. 
7. The necessity for strict empiricism in this method is emphasized, and the 
method in detail is given, involving the modifications presented in this paper. 
LITERATURE CITED 
(1) Benedict, S. R. 
1922. A METHOD FOR THE PURIFICATION OF PICRIC ACID FOR CREATININE 
determinations. Jour. Biol. Chem. 54: 239-241. 
(2) - and Osterberg, E. 
1918. A METHOD FOR THE DETERMINATION OF SUGAR IN NORMAL URINE. 
Jour. Biol. Chem. 34: 195-201. 
