48 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



may be quantitatively oxidized to aldonic acids, while the 

 former remain nearly or quite unattacked. Atkins and 

 Wilson have tested the possibility of employing oxidation 

 with bromine in the quantitative estimation of mixtures 

 of sucrose, maltose, glucose, and fructose. They found 

 that, after standing eight days in the dark in a solution 

 saturated with bromine, fructose remains almost entirely 

 untouched, as shown by its reducing action on Kendall's 

 solution. The removal of excess of bromine was effected 

 before analysis, by the cautious addition of sulphurous 

 acid till the solution became colourless. Blank experi- 

 ments show that, in the absence of sugars, the above 

 procedure does not give rise to any reduction. 



Maltose, on the other hand, is completely oxidized, and 

 glucose is almost entirely destroyed. Sucrose is inverted 

 during (or before) the bromine treatment, and the glucose 

 it yields is oxidized, but the fructose remains. 



Thus it is clear that, by means of bromine, glucose and 

 maltose may be largely removed, also the glucose resulting 

 from sucrose. Accordingly the reducing-power of the final 

 solution is due mainly to fructose. Since the sucrose can 

 be determined separately by inversion wifch invertase, it is 

 possible to subtract from the total fructose that which arose 

 from sucrose. In this manner the reducing-power due to 

 the fructose originally present can be approximately deter- 

 mined, and since the sucrose is already known, it remains 

 only to determine the glucose and maltose. For these, 

 after making the proper allowances for sucrose and fruc- 

 tose, both the values of optical activity and reducing-power 

 are known, and so, having two equations and two unknowns, 

 a solution can be obtained by the ordinary algebraical 

 methods. 



For purposes of accurate analysis, however, it is not 

 allowable to assume that fructose is untouched. For 



