56 



CARNEGIE INSTITUTION OF WASHINGTON. 



There is always a slight loss of iodine independent of the oxidation reaction; 

 this amount must be determined in a blank experiment in each determination 

 and allowed for. Three times the amount of iodine necessary to oxidize the 

 sugar is required to give a complete reaction. Within limits, dilution of the 

 iodine has no effect on the rate or completeness of the oxidation; as long as 

 there is sufficient excess of iodine present the concentration of the solution is 

 not significant. Because of the tendency of free iodine to escape the tempera- 

 tures of the reacting mixture above 25° are to be avoided. It was also found 

 desirable to carry out the oxidations in the dark, as avoidance of hght is as 

 important as temperature-control on the stability of the iodine solution. The 

 iodine solution was standardized in terms of glucose by means of the U. S. 

 Bureau of Standards glucose, dried in vacuum over phosphorus pentoxide. 



The oxidation of glucose in the presence of small or large amounts of levulose 

 proceeds without being influenced by the levulose. This is also true when 

 sucrose is used in place of levulose. This method can be used to determine 

 the amount of glucose and sucrose present together, by oxidizing the glucose 

 present before and after inversion. In order to avoid the action of the acid 

 on levulose in the course of inversion, a series of experiments established that 

 the best conditions for this is 1 per cent hydrochloric acid at 60° for 2 hours. 



Finally, iodine oxidizes glucose but not levulose; cupric hydroxide oxidizes 

 both sugars. The use of these two reagents with the method previously 

 worked out, and the present one, enables a determination to be made of glu- 

 cose, levulose, and sucrose when these three sugars occur together. The 

 copper solution must be standardized for both glucose and levulose ; the factor 

 to convert levulose, calculated as glucose, was found to be 0.9033. Thus, 

 in such a mixture the following results were obtained: 



Maltose can also be brought into the scheme of analysis, though it is found 

 much less frequently in plants. Sucrose is hydrolyzed five times more quickly 

 than is this sugar. Under the conditions used to invert sucrose there is no 

 effect on the maltose, so that advantage is taken of this fact in the analji;i- 

 cal separation of these two sugars. Maltose is best hydrolyzed with maltase. 

 However, some difficulty has been encountered in the use of this enzyme, so 

 that this portion of the method is still to be perfected. The calibration of the 

 copper solution for maltose has shown that 1 c. c. Benedict solution equals 

 3.583 mg. maltose, and to convert maltose, calculated as glucose, the factor 

 1.5052 should be used. 



