106 L^EYULOSE. GALACTOSE. 



verted into a true dextrin which may be precipitated by the addition of alcohol, and 

 is capable of reconversion into dextrose by mineral acids 1 . 



2. Laevulose. 



C 6 H 12 O 6 - [CH 2 . OH - CO - (CH. OH) 3 - CH 2 . OH]. 

 This is the ketone corresponding to the aldehyde dextrose. It is 

 best known as occurring mixed with dextrose in many fruits, also in 

 honey, and is stated to occur occasionally in urine. It is a characteristic 

 product of the action of dilute mineral acids on cane-sugar which is 

 hereby decomposed into equal parts of dextrose and Isevulose, and since 

 when the change is complete, the original dextro-rotatory power of the 

 solution has become Isevo-rotatory, the cane-sugar is said to have been 

 ' inverted.' A similar inversion takes place in the stomach and small 

 intestine (see under cane-sugar). In its general reactions Isevulose 

 behaves like dextrose, but may be at once distinguished from the latter 

 by its powerful Isevo-rotatory action on polarised light : this varies 

 considerably with the temperature and concentration of the solution. 

 It yields with phenyl-hydrazin an osazone identical with that derived 

 from dextrose. It forms a compound with calcium hydrate which 

 unlike that yielded by dextrose is extremely insoluble and may thus be 

 employed for the separation of the two sugars. 



3. Galactose (Cerebrose) C 6 H 12 6 . 



When milk sugar (lactose), see p. 113, is boiled with dilute mineral 

 acids it is decomposed into a molecule of dextrose and one of galactose 



C 12 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 12 6 . 



The two sugars may be separated by crystallisation and by taking 

 advantage of the greater solubility of galactose in absolute alcohol 2 . 

 In its general reactions and behaviour galactose resembles dextrose 

 but is possessed of a considerably greater specific rotatory power 

 [(a) D = + 83] which increases with the concentration and rise of 

 temperature 3 . It yields with phenyl-hydrazin an osazone (phenyl- 

 galactosazone) which has the same composition as phenyl-glucosazone 

 and very similar solubilities. It differs however from the latter in 

 melting at 190 193 and in being optically inactive when dissolved 

 in glacial acetic acid. It has recently been shown that the sugar 

 which was described by Thudichum 4 as resulting from the action of 

 boiling dilute sulphuric acid on certain constituents of the brain 



1 Musculus u. Meyer, Zt. f. physiol. Chem. Bd. v. (1881), S. 122. 



2 Fudakowski, Ber. d. d. chem. Gesell Jahrg. 1875, S. 599. Soxhlet, Jn. f. pr. 

 Chem. (2) Bd. xxi. (1880), S. 269. 



3 Meissl, Jn. f. pr. Chem. Bd. xxn. (1880), S. 97. 



4 Jn. f. pr. Chem. Bd. xxv. (1882), S. 19. 



