ESTIMATION 131 



The inversion of cane sugar may be represented thus : — 



CijHjjOii + HgO = CgHi^Og + CgHjgOg 

 The molecular weight of cane sugar is 342, and the amount 

 of invert sugar this will give on inversion is, from the equation, 

 360. In other words, i gram of glucose corresponds to ^i% 

 = -95 gram of cane sugar. The titration result must therefore 

 be multiplied by -95 ; otherwise stated : — 



10 c.c. Fehling's = -0475 gram sucrose. 



Estimation of Maltose. 



The reducing power of maltose is only 62 per cent of that 

 of glucose, hence since i gram maltose has the same reducing 

 power as 0-62 gram glucose, the equivalent of 10 c.c. Fehling's 



solution, which is 0-05 gram glucose, will be ,-^ = -oSl. 



Hence 10 c.c. Fehling's = -oSi gram maltose. 



An alternative method of estimating maltose, suitable in 

 the presence of glucose, is to find the number of cubic centi- 

 metres of Fehling's solution equivalent to lOO c.c. of the maltose 

 solution before and after hydrolysis ; this number of cubic centi- 

 metres X -005 gives the number of grams of glucose which, when 

 multiplied by 2-32, gives the number of grams of maltose. 



The figure 2-32 is arrived at from the following considera- 

 tions :— 



From the equation representing the inversion of maltose, 



it may be found that i gram of maltose gives 1-05 gram of 



glucose ; and, as i gram of maltose has the same reducing 



power as -62 gram of glucose, it follows that i gram of maltose 



after inversion gives an increased reducing power, viz. : — 



1-05 — -62 — -43 gram glucose, 

 ,•. '43 gram glucose = i gram maltose, 



and I gram glucose = — gram maltose, 



■43 

 = 2-32 grams maltose. 



The above method of acid hydrolysis which requires 

 heating at 100° for ninety minutes, cannot be employed if 

 cane sugar or levulose are present, since it is not possible to 

 hydrolyse maltose completely even at 70° in presence of cane 

 sugar or levulose without destroying a considerable quantity 



