106 L^VULOSE. GALACTOSE. 



dextrin which may be precipitated by the addition of alcohol, and is 

 capable of reconversion into dextrose by mineral acids. 1 



2. LaDvulose 



C 6 H 12 6 . [CH 2 . OH CO (CH. OH) 8 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 dex- 

 trose and laevulose, and since when the change is complete the 

 original dextro-rotatory power of the solution has become leevo- 

 rotatory, the cane-sugar is said to have been ' inverted.' A simi- 

 lar inversion takes place in the stomach and small intestine (see 

 under cane-sugar). In its general reactions lasvulose behaves like 

 dextrose, but may be at once distinguished from the latter by its 

 powerful Isevo-rotatory action on polarised light : this varies con- 

 siderably 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. 



2. 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 



Ci 2 H 22 O n -{- H 2 ^ C 6 Hi 2 Oe -f- C 6 H 12 O 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 =-f~ 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 cer- 



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



2 Fudakowski, E'er. d. d. chem. Gesell. Jahrg. 1875, S. 599. Soxhlet, Jn. f. pr. 

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



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



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



