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A. I. RINGER AND E3UL J. BAUMANN 



prepared solution, this change will take place in a few minutes. This 

 phenomenon was first observed by Duhriinfaut in 1840. By crystallizing 

 ordinary commercial glucose from different solvents and by other methods, 

 two different glucoses have been obtained, having specific rotatory powers 

 of + 100 and -<- 11) respectively. If either of these is dissolved in water, 

 it will slowly change its specific rotation to -f- 52.5. This phenomenon 

 is termed mut a rotation or birotation. 



Tanret, in 1S05 and 1806, was the first to demonstrate that we were 

 here dealing with more than one form of glucose. He called the glucose 

 with the high initial specific rotation a glucose, and the glucose of the 

 specific rotatory power 52.5 he designated (^-glucose. However it has 

 been found that Tanret's p-glueose was really a mixture obtained by 

 allowing the glucose of high or low rotatory power to reach equilibrium. 

 This happens when there are present 37 per cent of ct-glucose and 63 per 

 cent of the glucose having the initial specific rotator)' power of + 19, 

 which is now called P-glucose. The equilibrated mixture of a-and P-glu- 

 cose is known as y-ghicose 



The difference in structure of a and (^glucose is due to the difference 

 in the positions of the hydrogen atom and hydroxyl group of the carbon 

 atom that is potentially aldehydic. It may be represented as follows : 



CH 2 OH 



a-Glucose 



iicoii 



CH 2 OH 

 P-Glucose 



The conversion of pne form to the other is assumed to take place by 

 the formation of an intermediary compound, the exact nature of which is 

 still a matter of dispiite. 



Isomerism of the Aldohexoses. The number of possible stereoiso- 

 meric forms of a substance can be calculated by the formula of Le Bel 

 and Vari't Hoff. Number 2 n , where n is the number of asymmetric 

 carbon atoms in the molecule. If the open chain formula of glucose is 

 examined it will be found that it has four asymmetric carbon atoms: 



