86 THE CARBOHYDRATES 



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 : 



CjaHjoOu + H 2 = aC 6 H 12 Q 6 



the rotatory power of the solution being thereby diminished. 



5. The aqueous solution is strongly dextro-rotatory : 

 a D = + 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- 

 mentable by yeast ; this statement is, however, probably not 

 strictly true, since pure cultures of yeast containing only 

 zymase, the active enzyme which produces alcoholic fermenta- 

 tion, have no action on maltose. Ordinary brewers' yeast, 

 however, contains maltase, which first hydrolyses maltose to 

 grape sugar, which is then fermented by zymase. Only sugars 

 containing six carbon atoms are fermentable by yeast (see 

 P- 378). 



ISO-MALTOSE. C 12 H 22 O U . 



Iso-maltose is a disaccharide which is isomeric with and 

 closely related to ordinary maltose, its optical activity, 

 a D = +139-140, being almost the same as that of mal- 

 tose ; it is formed, together with ordinary maltose, when 

 diastase acts on starch, provided the enzyme is not present in 

 too large a quantity ; the most favourable temperature for its 

 production is 65-70. Iso-maltose is also formed together 

 with dextrin by the action of concentrated hydrochloric acid 

 on glucose at a temperature of 10-15, which accounts for the 

 fact that it is not infrequently met with as an impurity in 

 commercial glucose prepared by the action of hydrochloric 

 acid on starch (see p. 74). 



CELLOBIOSE. C U H W O U . 



This is a disaccharide obtained from cellulose by the 

 action of glacial acetic acid and acetic anhydride in the presence 

 of concentrated sulphuric acid. The resulting acetyl derivative, 



