730 CA R BO HYDRA TES. [App. 



2. Maltose. C 12 H 23 O n + H 2 O. 



This form of sugar was first described by Dubrunfaut 1 as a product 

 of the action of malt extract on starch. Its existence was for a long time 

 doubted until O'Sullivan 2 repeated and confirmed the previous experi- 

 ments. According to him it crystallises in fine acicular crystals, 

 possesses a specific rotatory power of + 150 and a reducing power which 

 is only one-third as great as that of dextrose. It seems probable that 

 this is the chief sugar obtained by the action not only of diastase but of 

 ptyalin and pancreatic ferment upon starch and perhaps also upon 

 glycogen 3 ; although some dextrose may at the same time be formed. 

 Musculus and Gruber 4 have shewn that maltose may also be formed by 

 the action of dilute sulphuric acid on starch, and that it is capable of 

 undergoing alcoholic fermentation. 



Preparation. See Musculus and Gruber (loc. cif.). 



3. Milk-sugar. C i2 H 22 11 + H 2 O. 



Also known as Lactose. It is found in milk, and is characteristic 

 of this secretion. It is said however to occur abnormally in the urine of 

 lying-in women 5 . 



It yields, when pure, hard colourless crystals, belonging to the 

 rhombic system (four-sided prisms). It is less soluble in water than 

 dextrose, requiring for solution six times its weight of cold, but only 

 two parts of boiling, water; it is entirely insoluble in alcohol and aether. 

 It is fully precipitated from its solutions by the addition of lead acetate 

 and ammonia. 



When freshly dissolved, its aqueous solution possesses a specific dextro-rotatory 

 power of +93-1 for sodium light: this diminishes, slowly on standing, rapidly on 

 boiling, until it finally remains constant at +52 '5. The amount of rotation is 

 independent of the concentration of the solution. 



Lactose unites readily with bases, forming unstable compounds ; from its metallic 

 compounds the metal is precipitated in the reduced state on boiling ; it reduces 

 copper salts as readily as dextrose but to a less extent viz. in the ratio of 70 : 100. 



Lactose is generally stated to admit of no direct alcoholic fermenta- 

 tion ; this may however sometimes be induced by the prolonged action 

 of yeast. By boiling with dilute mineral acids lactose is converted into 

 galactose, which readily undergo alcoholic fermentation and possess a 

 greater rotatory power than lactose. 



It may be remarked here that though isolated lactose is incapable of direct 

 alcoholic fermentation, milk itself may be fermented; Berthelot was unable in this 



1 Ann. Chim. Phys. (3) xxi. (1847), p. 178. 



2 Jl. Chem. Soc. Ser. 2, Vol. x. (1872), p. 579. 



3 Musculus u. v. Mering, Zeitsch.f. physiol Chem. Bd. n. (1878), S. 403. 



4 Zeitschr. f. physiol. Chem. Bd. n. (1878), S. 177. 



5 Hofmeister, Ibid. Bd. i. (1877), S. 101. 



