ii6 THE CARBOHYDRATES 



•25-2 per cent of dry weight, which obtain in the different 

 phases of the life-history of the plant, he concludes that 

 maltose, in this instance, is not a transitional sugar but a 

 true reserve material comparable to starch and sucrose. In 

 the germination of the barley maltose is produced, but it does 

 not accumulate owing to the action of maltase which, as has 

 already been stated, converts it into hexose. 



Maltose is also formed by the action of diastase and other 

 enzymes on glycogen. 



In preparing maltose from starch, 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]2H220ii, H2O ; its aqueous solution is strongly dextro- 

 rotatory : ai3=+ 137°; freshly made solutions exhibit a 

 higher rotation than older ones, owing to a negative muta- 

 rotation. 



1. Maltose reduces Ny lander'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 75 parts of boiling water, and can be crystallized 

 from this solvent in rosettes of plates or broad needles 



