72 



Scientific Proceedings (72). 



is heated to boiling over a free flame and then placed in a boiling 

 water-bath for ten minutes. If levulose is present, a yellow color 

 appears which is deeper for greater concentrations of the sugar. 

 A yellow precipitate settles out on cooling. Upon the addition of 

 alkali (KOH or NaOH) sufficient to neutralize the phosphoric 

 acid, the yellow color changes to a distinct orange. The char- 

 acteristic orange color developed was made the basis for the quan- 

 titative determination of levulose. 



The procedure for the quantitative test is essentially the same. 

 The standard for colorimeter comparison is a definite known 

 solution of levulose in distilled water. The strength of the 

 standard is arbitrary but should be as near the concentration of 

 the unknown solution as possible to favor a more accurate com- 

 parison. Hence the advisability of performing a preliminary 

 test to determine the optimum standard. The standard and un- 

 known solutions are similarly treated, to 1 c.c. of each in separate 

 test tubes add 8 drops of the orcein solution and I c.c. of phosphoric 

 acid. The solutions are, as before, boiled over a free flame and 

 heated in a boiling water-bath for ten minutes. The test tubes 

 are then removed and the contents of each are transferred quanti- 

 tatively to separate ten c.c. volumetric flasks and made up to the 

 mark with 5 N NaOH. The solutions are at once placed in the 

 colorimeter chambers and the orange colors compared. 



Results. 



Qualitative. — Levulose was detected in 1 c.c. of a 0.005 per cent, 

 solution. 



A positive reaction was obtained from 0.5 c.c. of a 0.01 per cent, 

 solution of levulose in the presence of 0.5 c.c. of a 20 per cent, 

 solution of dextrose. 



Maltose, lactose, galactose, and R. arabinose in solutions of 

 various strengths did not interfere with the test. 



Cane sugar yielded a positive test, due to the presence of 

 levulose from the hydrolytic cleavage of the sugar in the presence 

 of the phosphoric acid. 



Quantitative. — The orange color was found to be characteristic 

 for the different concentrations of levulose. Uniformly good results 

 were obtained with unknown solutions in the presence of various 

 amounts of glucose. 



