486 
Journal of Agricultural Research 
Vol. XXVIII, No. 5 
exactly 1 cc. of unknown sugar solution, 2 cc. of saturated picric acid, and 1 cc. 
of 20 per cent sodium carbonate. 
During the 30 minutes of heating in a water bath, evaporation of water from 
the sugar tubes may be prevented (1) by loosely inserting corks covered with 
tinfoil in the tops of the tubes; and (2) by keeping the level of water in the bath 
approximately at the same level as the solutions in the sugar tubes. A wire rack 
fitting into a basin is a very convenient holder for the tubes. 
Thus it will be seen that the conditions involved in determining sugar by this 
method are rather empirical. The writers believe that extreme empiricism is 
the only feasible basis for any colorimetric method. A given procedure and set 
of conditions must be decided upon, and then rigidly adhered to, whether they 
give maximum color intensities or not. The unknown color will he exactly com¬ 
parable to the known, since they were both produced under exactly the same 
conditions. From this standpoint the most significant points in the present 
method are the effect of heat and picric acid on glucose, the use of the table of 
factors, and the use of exact amounts of reagents. 
PROPOSED METHOD IN DETAIL 
SOLUTIONS 
1. Saturated picric acid that has been recrystallized from hot dilute hydro¬ 
chloric acid. 
2. Twenty per cent sodium carbonate (anhydrous). 
3. An 0.08 per cent standard glucose solution, either in water or in saturated 
picric acid, as discussed above. An 0.076 per cent sucrose solution is equally 
suitable, and has the same color value. 
PREPARATION OF MATERIAL 
If it is known that lead clarification has no effect on the results with the sugar 
solution in question, no clarification is needed. Otherwise the usual lead acetate 
clarification should be performed, followed by deleading with disodium phos¬ 
phate. The solution is then diluted until both the sucrose and the reducing 
sugars are between 0.02 and 0.24 per cent. 
REDUCTION 
1. Reducing sugars. —One cubic centimeter of the diluted sugar solution is 
pipetted into a sugar test tube, followed by 2 cc. of picric acid and 1 cc. of 
sodium carbonate. The solutions are thoroughly mixed and the tube lightly 
stoppered with a cork covered with tinfoil. The tubes are then immersed in 
boiling water for 20 to 30 minutes. They are then cooled and the contents 
diluted to the 10 cc. mark and shaken. 
2. Total sugars. —One cubic centimeter of the diluted sugar solution and 2 cc. 
of picric acid are pipetted into a sugar test tube and immersed in boiling water 
for 10 minutes. Then 1 cc. of sodium carbonate solution is added, the mixture 
shakbn, and the heating continued for 20 to 30 minutes. Cooling, mixing, and 
diluting are then conducted as stated above. 
3. Standard color. —One cubic centimeter of the standard glucose or sucrose 
solution is treated the same as for total sugars. 
