70 THE CARBOHYDRATES 



Maltose is also formed by the action of diastase and other 

 enzymes on glycogen. 



In preparing maltose from starch, it is not necessary 

 always to act on the starch contained in barley, potato-starch 

 serving equally well, the diastase which is employed is usually 

 introduced in the form of malt, which is barley that has been 

 allowed to sprout and is then killed by suddenly heating to a 

 temperature sufficient to stop the further growth of the barley 

 without destroying the diastase. The malt is then stirred up 

 with starch and water, and kept at a temperature of 60-62° 

 for about half an hour ; by the end of this time about 80 per 

 cent of the starch has been converted into maltose and 20 per 

 cent into dextrin. Dextrin itself is also converted into maltose 

 by diastase, but the reaction is very slow, and in practice 

 sufficient time is not allowed to effect this change. 



Properties and Reactions. 



Maltose is readily soluble in water, and crystallizes from 

 this solvent in slender white needles, having the composition 



C,,H,Ai- H,0. 



1. Maltose reduces Nylander's reagent, but not Barfoed's 

 reagent. 



2. Maltose reduces Fehling's solution without previous 

 hydrolysis, and can therefore be estimated directly by this 

 means. 



3. When treated with phenylhydrazine, as described under 

 glucose, it gives an osazone (m.p. 206°), which is soluble in 

 seventy-five parts of boiling water, and can be crystallized 

 from this solvent in rosettes of plates or broad needles re- 

 sembling sword blades ; alcoholic solutions of maltosazone 

 are dextro-rotatory. (Distinction from glucosazone.) 



4. On hydrolysis, by boiling with dilute sulphuric acid, 

 maltose breaks up into two molecules of glucose: — 



C12H22O11 + HjO - aCgHioOH 



the rotatory power of the solution being thereby diminished. 



5. The aqueous solution is strongly dextro-rotatory : 

 an = + 137°; freshly-made solutions exhibit a higher rota- 

 tion than older ones, owing to a negative muta-rotation. 



6. Unlike cane sugar, maltose is said to be directly fer- 



