218 GLUCOSES, SACCHAROSES, ETC. 



amount of grape-sugar present from the rotation observed. For 

 anhydrous dextrose Tollens and v. Grote^ ascertained {a)-^ = 53 '10°, 

 and the constant quantity = 1883-3. Hesse has shown that the 

 prolonged heating of aqueous sohitions of dextrose reduces the 

 angle of rotation still further. 



Biot has asserted the existence of glucoses, agreeing with grape- 

 sugar in all important properties, but differing from it in their 

 rotatory power ; and the truth of this assertion has been proved 

 by Hesse. An instance may be cited in saUcin-sugar, the crystalline 

 modificationof which possesses a rotatory power (a)p = 100° (p = 1), 

 and the amorphous {u)jy = 50° (populin-sugar is said to correspond 

 to ordinary dextrose) ; the rotatory power of jMorose from phloricin 

 is five-sixths that of glucose. - 



Fruit-sugar (levulose) has recently been obtained in acicular 

 crystals;^ a freshly prepared solution shows a rotatory power 

 (a)j)= -106° (constant 943-4; see also note to §209), which 

 slowly diminishes, on boiling, to —56°. Levulose dissolves more 

 easily in alcohol than crystalline dextrose, which may therefore, to 

 a certain extent, be freed from the former by washing with spirit. 

 The disposition to form a sparingly soluble compound Avith lime 

 is very characteristic of levulose, and forms, at the same time, a 

 means of separating this from grape and other sugars. Like 

 dextrose, levulose is fermentable ; but when both sugars are 

 present together, the former is the first to undergo alcoholic 

 fermentation. 



Sugars allied to levulose, differing from it only in the rotatoiy 

 power, will probably be found in certain plants (Jerusalem arti- 

 chokes, etc. ; see also § 199). 



Invert-sugar (see also § 209 ct seq.) shoAvs as a rule a rotatory 

 power for («)„ of — 18°. The majority of chemists regard it as a 

 mixture of grape- and fruit-sugar, molecule for molecule ; but 

 Maum6n6* differs from them, and maintains that he has found in 

 it, in addition to these two constituents, another, optically in- 

 active, unstable sugar. 



1 Ber. d. d. chem. Ges. 487, 616, If^Sl, 1876. See also Hesse, Annal. d. 

 Cjiem. und rharm. cxcii. 169, 1879. 



" Compare Hesse, Annal. d. Chem. und Pharm, cxcii. 173, 1878. 



^ Jungfleisch and Lefranc, Comptes rendus, xciii. f>i7. 



* Journ. d. Pharm, et de Chim. xxii. 47, 1875. The name of chylariose has 

 been given by Maumenö to the IjEvo-rotatory constituent of invert-sugar. 



