AND POLYHYDRIC ALCOHOLS 163 



melted at 80-82 and behaved as a glucoside towards Fehling's 

 solution. The specific rotation in aqueous solution was 

 + 142'6 a value which is practically identical with that 

 found for a solution in acetone. 



When boiled for 30 minutes with 10 per cent, hydrochloric 

 acid, the glucosidic group was removed, and, on working up 

 the product, dimethyl glucose was obtained in the form of a 

 syrup which gradually crystallised on standing. After crystal- 

 lisation from ethyl acetate, the sugar was obtained in the 

 form of well-developed prisms which gave satisfactory 

 analytical figures but which melted very indefinitely. This 

 behaviour was shown to be due to the presence of the stereo- 

 isomeric a- and /3-forms, both of which were ultimately 

 separated. 



When the crystallisation from ethyl acetate is carried out 

 with solutions containing not more than five per cent, of the 

 solute, the sugar separates in clusters of delicate pointed 

 prisms. This is the pure /3-form (m.p. 108-110) and thus 

 shows upward mutarotation when dissolved. 



Solvent. c. Change in Specific Rotation. 



Water . . . 5'00 +10-6 -- - +64-4 



Alcohol ... 5-02 5-7 49" 4 



Acetone. . . 3'84 6'5 > 50'9 



The compound showed the phenomenon of suspended 

 mutarotation in acetone solution, and it was thus possible 

 to obtain an exact record of the whole range of the optical 

 change in this solvent. 



The a-form of the sugar separates, along with the 

 /3-isomeride, from solutions in ethyl acetate containing from 

 5 to 10 per cent, of the solute. Separation of the two varieties 

 was, however, effected by cautious precipitation from the equi- 

 librium solution in alcohol by the gradual addition of ether. 

 The first crops to separate consisted as before of the /8-form, 

 but from the mother liquors the a-isomeride (m.p. 85-87) was 



