§§ 85— 87. INFLUENCE EXEMTED BY SA CCHABOSES. 75 



The reagent is said to be without action on cane-sugar, glycerin, 

 arabin and dextrin. 



§ 85 — hfiuence exerted ly Stuxkarases. — If the glucose in the 

 liquid under examination is not accompanied by aaccharose, or 

 other carbohydrate not precjpitable by alcohol, fairly accurate 

 resulta may be obtained by the methods detailed in §§ SS^ 84. 

 But saccharoses influence the estimation by their presence to an 

 appreciable extent, although they do not themselves, when pure, 

 reduce Fehling's or Sachsse's solution. 



The same applies to the determination by fermentation (§204); 

 saccharoses may be pajtiaUy converted by the yeast into ferment- 

 able glucose. 



It cannot be said that we are in a position to estimate with 

 exactness in' every case the proportion of glucose and saccharose 

 in mixtures Sometimes, it is true, the accuracy of the estimation 

 leaves little to be de.*i,*d— as, for example, mixtures of dextrose 

 or invert-sugar with cane-sugar. Solutions of such mixtures 

 may be examined in the polariscope, in addition to being ested ' 

 chemically. -- But many instances occur in which the neccesary 

 conditions de not obtain. (Cf. §§ 208, 209.) 



§ SSr-Estirmtion in Presence of Saccharose. — In such cases the 

 only method we can adopt is, first, to remove the carbohydrates 

 precipitable by alcohol (^ 73, 76), estimate the glucose with 

 Fehling's solution, and then repeat the estimation after acidifying 

 with 1 per cent, hydrochloric acid and boiling for 15 to 20 minutes 

 (or several hours if the presence of mycose be suspected) fa a flask 

 provided with an upri^t condenser. If the two determinations 

 yield fairly concordant results, it may be assumed that no saccha- 

 rose is present ; on the other hand, any excess that the second 

 may indicate over the first may be noted as saccharose or allied 

 carbohydrate.' The possibility of error must, however, be 

 admitted (§ 207). 



§ 87. Estimalion of Saccharose alone. — If the solution contains a 

 saccharose alone, with the exception of millo-sugar or maltose, it 

 will not reduce Fehling at all. Although, therefore, no reduction 

 may be observed, the inversion with acid should not on any account 

 be omitted, as the solution may contain a saccharose. (Cf. § 207.) 



According to PiUitz,* cane-sugar may be easily inverted by 



1 2eitaclir. f. anal. Cheraie. x. 456 (Journ. Chem. Soc. xxv. 329). See also 

 Nicol. ib. xiv. 177 (Journ. Chem. Soc. xxv, 370). 



