84 THE CARBOHYDRATES 



converting it into equal molecular proportions of the two 

 sugars dextrose and levulose, 



C 12 H 2i Ai + H 2 = C 6 H 12 6 + C 6 H 12 6 



and since the optical activity of levulose is greater than that 

 of dextrose the resulting invert sugar is laevo-rotatory. 



Numerous experiments have been carried out with a view 

 to determining the conditions which bring about this inversion. 

 Aqueous solutions of cane sugar, if kept for some time, gradually 

 become inverted, the change being somewhat accelerated by 

 prolonged boiling. 



Similarly cane sugar solutions when heated with acids 

 undergo inversion, the rate at which the change takes place 

 being a measure of the strength, or better, the chemical affinity, 

 of the acid. Extremely small quantities of acid suffice to 

 effect the change in a boiling solution ; thus 80 parts of cane 

 sugar dissolved in 20' parts of water are completely hydro- 

 lysed by heating in boiling water for one hour with an amount 

 of hydrochloric acid corresponding to 0-005 per cent of the 

 weight of the sugar ; within certain limits, however, the action 

 is accelerated by increasing the concentration of the acid. If, 

 however, the acid is too strong and the heating be continued 

 too long, the solution is liable to darken and decompose. 

 Moreover, prolonged action, even at temperatures of 10-15, of 

 concentrated acids was found by Wohl * and by Fischer f to 

 produce exactly the opposite phenomenon, known as reversion, 

 by which the simple molecules, more especially those of levu- 

 lose, are made to condense together to form complex dextrin- 

 like substances, as well as a disaccharide isomaltose. 



6. Sucrose is not directly fermentable by pure yeast. 



TURANOSE. C^H^OH. 



This is a disaccharide formed by the partial hydrolysis of 

 the trisaccharide melecitose (see p. 91); it reduces Fehling's 

 solution, and on hydrolysis yields glucose and levulose; it is 

 therefore isomeric with sucrose. 



* Wohl: " Ber. deut. chem. Gesells.," 1890, 23, 2092. 

 t Fischer : id., 1890, 23, 3687. 



