1222 MALTOSE. 



Cane-sugar readily undergoes a lactic-acid fermentation in 

 presence of sour milk to which zinc oxide is added for the fixa- 

 tion of the acid as it is formed. 



2. Maltose. C 12 H 22 O U + H Z O. 



This is the sugar which is characteristically formed, together 

 with dextrins, by the action of malt-extract (diastase) on starch- 

 paste. It is similarly the chief sugar which is formed by the 

 action of saliva and pancreatic juice upon starch-paste or upon 

 glycogen, being accompanied in the case of pancreatic juice by 

 a variable but distinct amount of dextrose if the action of this 

 secretion be prolonged. Maltose is also formed by the action 

 of dilute acids upon starch-paste, but in this case it is difficult 

 to prevent the simultaneous formation of dextrose, into which 

 it is readily converted by acids, yielding 98 99 p.c. of the 

 latter sugar. It is therefore usually prepared from the products 

 of the action of malt-extract on starch-paste. 



Maltose is very soluble in water, also in alcohol, but less so 

 in the latter solvent than is dextrose. It crystallizes in fine 

 needles which are however not very easily obtained. Solutions 

 of maltose are dextrorotatory and reduce metallic salts ; it is 

 therefore not easily distinguished from dextrose by merely 

 qualitative tests. As the necessity of discriminating between 

 the two sugars is one of frequent occurrence, the following 

 characteristic differences between their optical and reducing 

 powers are of great importance. For maltose in 10 p.c. solu- 

 tion at 20 C. (),,= + 140 ; 1 for dextrose () D = + 52-5. 

 When maltose is boiled with Fehling's fluid 2 the amount of 

 cuprous oxide which separates out is only about two-thirds of 

 that which would be reduced by an equal weight of dextrose, 

 or in other words 66 parts of dextrose reduce as much as 100 

 parts of maltose. Bearing in mind that maltose may be readily 

 converted into dextrose by boiling with dilute acids with a cor- 

 responding change of its optical and reducing powers, while 

 dextrose is of course unaltered by this operation, it is easy to 

 base upon the above facts a method of identifying the two 

 sugars. As a further difference between the two it may be 

 stated that Barfoed's reagent 3 is not reduced by maltose, whereas 

 it is by dextrose. In this respect maltose resembles lactose 

 (milk-sugar) which also does not reduce this reagent. 



Phenyl-maltosazone. C 24 H 32 N 4 O 9 . 



This compound of maltose is obtained by the action of 



1 Some authors make it less = + 135-4. 



2 Solution of hydrated cupric oxide in caustic soda in presence of the double 

 tartrate of sodium and potassium (Rochelle salt). 



3 Dissolve 1 part of cupric acetate in 15 parts of water: to 200 c.c. of this 

 solution add 5 c.c. of acetic acid containing 38 p.c. of glacial acid. 



